Sounds like a quest specific bug that needs to be reported to the Cobl team so an exception can be made in that circumstance.
Fortunately, I just bumped the Cobl thread to the top, so it should be easy to find.
Active Mod Files:00 Oblivion.esm01 Francesco's Leveled Creatures-Items Mod.esm02 Francesco's Optional New Items Add-On.esm03 Cobl Main.esm [Version 1.72]04 Oscuro's_Oblivion_Overhaul.esm [Version 1.34]05 Mart's Monster Mod.esm [Version 3.7b3p3]06 TamrielTravellers.esm [Version 1.39c]07 FCOM_Convergence.esm [Version 0.9.9MB3]08 Armamentarium.esm [Version 1.35]09 Artifacts.esm [Version 1.1]0A Progress.esm [Version 2.2]** TNR ALL RACES FINAL.esp0B Unofficial Oblivion Patch.esp [Version 3.2.4]0C UOP Vampire Aging & Face Fix.esp [Version 1.0.0]0D DLCShiveringIsles.esp0E Unofficial Shivering Isles Patch.esp [Version 1.4.0]0F SI Public Music.esp10 Francesco's Optional Chance of Stronger Bosses.esp11 Francesco's Optional Chance of Stronger Enemies.esp12 Francesco's Optional Chance of More Enemies.esp13 Francesco's Optional Leveled Quests-SI only.esp14 Francesco's Optional Leveled Guards.esp++ FCOM_Francescos.esp [Version 0.9.9]++ FCOM_FrancescosItemsAddOn.esp [Version 0.9.9]15 FCOM_FrancescosNamedBosses.esp [Version 0.9.9]16 Fran Armor Add-on.esp17 Fran_Lv30Item_Maltz.esp18 FranOBSEConfig.esp [Version 0.5]19 Atmospheric Loading Screens - Random Quotes.esp++ oc_darker_nights.esp1A Improved Water.esp1B Better Bell Sounds.esp1C ln.esp++ Symphony of Violence.esp1D Echo_ChapelChant.esp1E AmbientTownSounds.esp1F MIS Low Wind.esp20 MIS New Sounds Optional Part.esp21 Atmospheric Oblivion.esp22 WindowLightingSystem.esp23 100%ChameleonMod.esp** Book Jackets Oblivion.esp24 Happyhannah's Wines.esp [Version 1.1]++ Item interchange - Extraction.esp [Version 0.78]25 P-Froggys Wall Climbing EV.esp26 Pitchable_Tent_anywhere.esp27 PrivateQuarters.esp [Version 2.33]28 Q - More and Moldy Ingredients v1.1.esp++ Regrowing Nirnroot - Dissappear Reappear.esp [Version 1.01]29 Wyverex's - Runes.esp2A Enhanced Economy.esp [Version 3.4.3]2B Map Marker Overhaul.esp [Version 3.3.1]2C Map Marker Overhaul - SI additions.esp [Version 3.0.2]2D HotkeyCasting.esp2E DLCHorseArmor.esp2F DLCHorseArmor - Unofficial Patch.esp [Version 1.0.5]30 DLCOrrery.esp31 DLCOrrery - Unofficial Patch.esp [Version 1.0.3]32 DLCVileLair.esp33 DLCVileLair - Unofficial Patch.esp [Version 1.0.5]34 DLCMehrunesRazor.esp35 DLCMehrunesRazor - Unofficial Patch.esp [Version 1.0.4]36 DLCSpellTomes.esp++ DLCSpellTomes - Unofficial Patch.esp [Version 1.0.1]** Book Jackets DLC.esp** GrimbotsSpellTomes.esp++ MaleBodyReplacerV4.esp37 GruntsSigilStones.esp38 Nicoroshi Creations DW Light.esp39 Nicos Kynareth Archery.esp [Version 1.0]** StockClothingArmor-forExnems.esp** Armamentium female.esp3A Mart's Monster Mod - Hemingweys NPC and Guard Capes.esp [Version 1.0]3B DLCThievesDen.esp3C DLCThievesDen - Unofficial Patch.esp [Version 1.0.5]3D DLCThievesDen - Unofficial Patch - SSSB.esp [Version 1.0.4]++ Francesco's No Reduced Backwards Running.esp3E KDCircletsOOOOptimized - NPC Equip.esp [Version 1.2]3F FCOM_KDCircletsOOOOptimizedNPCEquip.esp [Version 0.9.9]40 Slof's Oblivion Robe Trader.esp41 Cobl Glue.esp [Version 1.72]42 Cobl Si.esp [Version 1.63]43 OOO 1.32-Cobl.esp [Version 1.72]++ FCOM_Cobl.esp [Version 0.9.9]44 Bob's Armory Oblivion.esp45 FCOM_BobsArmory.esp [Version 0.9.9]46 Oblivion WarCry EV.esp47 FCOM_WarCry.esp [Version 0.9.9MB3]48 Oscuro's_Oblivion_Overhaul.esp [Version 1.34]++ OOO-Water_Weeds.esp [Version 1.33]49 OOO-No_Guild_Ownership.esp [Version 1.33]++ OOO-DLT_Remover.esp [Version 1.33]++ ArmamentariumLLVendors.esp [Version 1.35]4A ArmamentariumArtifacts.esp [Version 1.35]4B FCOM_Convergence.esp [Version 0.9.9Mb3]++ FCOM_EntropicOrderRebalance.esp [Version 0.9.9beta2]4C FCOM_RealSwords.esp [Version 0.9.9]4D FCOM_DurabilityAndDamage.esp [Version 0.9.9]4E Mart's Monster Mod - More Wilderness Life.esp [Version 3.7b3p3]++ FCOM_LessRats.esp [Version 0.9.9]4F Mart's Monster Mod - Extra Wounding.esp [Version 3.7b3p3]++ Mart's Monster Mod - Looting NPCs & Creatures.esp [Version 3.7b3p3]50 Mart's Monster Mod - No Carrion Rats.esp [Version 3.7b3p3]++ Mart's Monster Mod - No Slimes.esp [Version 3.7b3p3]++ Mart's Monster Mod - Less Bone Loot.esp [Version 3.7b3p3]51 Mart's Monster Mod - Zombies for Body Meshes.esp [Version 3.7b3p3]52 Mart's Monster Mod - Safer Quest Locations.esp [Version 3.7b3p3]53 Mart's Monster Mod - Dungeons of MMM.esp [Version 3.7b3p3]54 Mart's Monster Mod - Gems & Gem Dust.esp [Version 3.7b3p3]55 Mart's Monster Mod - Hunting & Crafting.esp [Version 3.7b3p3]56 Mart's Monster Mod - Farm Animals.esp [Version 3.7b3p3]57 Mart's Monster Mod - Diverse WaterLife.esp [Version 3.7b3p3f]58 MMM - Playable Undead Armors.esp++ MMM - Playable Undead Armors - Oblivion WarCry Compatability Patch.esp++ Mart's Monster Mod - Slof Horses Complete.esp [Version 3.7b3p3]++ Mart's Monster Mod - Diverse Runeskulls Loot G&GD.esp [Version 3.7b3p3]++ TamrielTravellerAdvscript.esp [Version 1.39c]59 TamrielTravellers4OOO.esp [Version 1.39c]5A TamrielTravellersItemsCobl.esp [Version 1.39c]5B ShiveringIsleTravellers.esp [Version 1.39c]++ ShiveringIsleTravellersFriendlyFactions4MMM.esp [Version 1.39c]++ FCOM_TamrielTravelers.esp [Version 0.9.9]++ FCOM_DiverseGuardUnity.esp [Version 0.9.9]++ FCOM_BobsGuardUnity.esp [Version 0.9.9]++ FCOM_HungersUnitySI.esp [Version 0.9.9]++ FCOM_Archery.esp++ FCOM_Archery_Armamentarium.esp++ FCOM_Archery_Artifacts.esp++ FCOM_Archery_RealSwords.esp++ FCOM_Archery_MMM_H&C.esp++ Mart's Monster Mod - Shivering Isles.esp [Version 3.7b3p3]++ ArmamentariumLL4OOO.esp [Version 2.01]++ ArmamentariumLLMagicOOO.esp [Version 1.35]** Fransfemale.esp** OOO-Armor.esp5C SSEE-OOO.esp5D OOO-No_Clutter_Ownership.esp++ MMM-Cobl.esp [Version 1.69]5E Artifacts.esp [Version 1.1]++ Artifacts - ArmaCompleteAddon.esp [Version 1.0]5F Bottomless Cavern.esp60 CryptofDecay.esp61 Forgotten Tomb.esp62 goldenarrowarcheryshopfixedprices.esp63 Shady Sam Plus.esp64 The Ayleid Steps.esp [Version 3.3]65 Unique Dungeons - Lichs Lair.esp66 DLCBattlehornCastle.esp67 DLCBattlehornCastle - Unofficial Patch.esp [Version 1.0.4]68 DLCFrostcrag.esp69 DLCFrostcrag - Unofficial Patch.esp [Version 1.0.4]++ DLCFrostcrag_MysticEmporiumPatch.esp6A Knights.esp6B Knights - Unofficial Patch.esp [Version 1.0.9]6C AFK_Weye.esp6D Blood&Mud.esp6E Blood&Mud - EE patch.esp [Version 1.0]6F Mart's Monster Mod - City Defences.esp [Version 3.7b3p3]70 FCOM_Blood&Mud.esp [Version 0.9.9]++ FCOM_Knights.esp [Version 0.9.9Mb3]++ FCOM_SlofsRobeTrader.esp [Version 0.9.9]++ FCOM_UnofficialFranArmorAddon.esp [Version 0.9.9]71 Harvest [Flora].esp [Version 3.0.0]++ Harvest [Flora] - Shivering Isles.esp [Version 3.0.0]++ Harvest [Flora] - DLCVileLair.esp [Version 3.0.0]72 Harvest [Flora] - DLCFrostcrag.esp [Version 3.0.0]73 Pitcher Plant and Lily Ingredients.esp74 DropLitTorchOBSE.esp [Version 2.1]75 DS Portable Sorters.esp [Version 1.1]76 DS Storage Sacks.esp [Version 1.21]++ more books teach.esp77 P1DkeyChain.esp [Version 5.00]78 Respawnable NPC Mod.esp79 Respawning Varla & Welkynd Stones.esp7A RTSWelkyndClstrTreasure.esp [Version 2.0]++ Enhanced Vegetation [100%].esp7B Toggleable Quantity Prompt.esp [Version 3.1.1]7C ATakesAll.esp7D Quest Award Leveller.esp++ Quest Award Leveller - Vile Lair.esp++ Quest Award Leveller - Mehrunes Razor.esp++ Quest Award Leveller - Knights of the Nine.esp7E Encumbrance100.esp7F EnchantmentMastery.esp80 RefScope.esp [Version 1.3.0]81 SupremeMagicka.esp [Version 0.90]82 SM_ShiveringIsles.esp [Version 0.86]++ SM_DLCSpellTome.esp [Version 0.80]++ SM_OOO.esp [Version 0.89]++ SM_MMM.esp [Version 0.89]++ SM_COBL.esp [Version 0.86]++ LightSpellWhiteDimmer.esp83 ArcaneArchery.esp84 RshAlchemy.esp85 RshAlchemyRecipes.esp86 Lightweight Potions.esp [Version 1.1]87 EnchantmentRestore.esp++ EnchantmentRestore_Wells.esp88 attack and hide medium v2.0.esp89 SM Bounty.esp [Version 1.21]++ CoblDeathFix.esp [Version 1.20]8A Enhanced Grabbing.esp [Version 0.4]8B ProgressMBSP.esp [Version 2.0]8C ProgressRBSP.esp [Version 1.0]8D Legendary Abilities-Reflect MOJ.esp8E Grandmaster of Alchemy.esp8F S.P.A.M. 100+.esp90 S.P.A.M. option - Faster Minor.esp91 S.P.A.M. option - Restore Fav.esp92 Let There Be Darkness - Cyrodiil + SI.esp93 Let There Be Darkness - Knights.esp94 Let There Be Darkness - Mehrunes Razor.esp95 Let There Be Darkness - Thieves Den.esp96 Let There Be Darkness - OOO.esp++ Item interchange - Placement for FCOM.esp [Version 0.78]++ Item interchange - Placement for Frostcrag.esp [Version 0.78]++ Item interchange - Option, Ingredients in Bulk.esp [Version 0.78]97 bgBalancingEVCore.esp [Version 10.52EV-D]98 bgMagicEV.esp [Version 1.7EV]++ bgMagicSpellTomes_for_WryeBash.esp [Version 1.68EV]++ bgMagicEVStartspells.esp [Version 1.68EV]++ bgMagicEVAddEnVar.esp [Version 1.68EV]++ bgBalancingEVOptionalFangs.esp [Version 10.0EV-D]++ bgBalancingEVOptionalMoreEyes.esp [Version 10]** bgBalancingEVOptionalNPCDiversity, TNR Merge.esp [Version 10.0EV-D]99 bgBalancingOptionalNoRaceDisp.esp [Version 9.0UV-U]++ bgBalancingEVOptionalFCOMAdditions.esp [Version 10.]++ bgBalancingEVOptionalSeamReducerHighElfFix.esp [Version 10.0EV-D]9A TheOubliette.esp++ [GFX]_Initial_Glow-all.esp9B bgMagicEVShader.esp [Version 1.7EV]++ Detect Life Shader [New].esp9C DS Flaming Arrows.esp [Version 1.2]9D qazFingerSnap.esp9E Shining Creatures.esp++ Shining Creatures_DLCFrostcrag.esp9F Hemingweys Capes.esp [Version 2.00]A0 MiniMap.espA1 Vacuity.esp [Version 0.2]A2 Cobl Silent Equip Misc.esp [Version 01]A3 Never die.espA4 Bashed Patch, 0.espA5 Duke Patricks - BASIC Script Effect Silencer.esp