In vanilla weapons are tied to bodies. In my modded game they are separated. But while bodies eventually disappear, weapons dont. Checked it, waited in room for 40 days, and sword dropped from foe still laying on the ground.

I have few questions:

1. Which mod does it?

2. Can this cause save bloat or other issues?

I don't know which mod is the culprit, for the reason, i don't know your mods. (I am not Harry Potter...lol)

However:

In the PC, this is fixed by the Unofficial Skyrim Patch ( http://www.darkcreations.org/forums/files/file/289-unofficial-skyrim-patch/ )

• Ghostly Remains, Ice Piles and Wisp Cores will no longer permanently remain and bloat the save file (they will either disappear on exit of the cell or when the cell resets).
• NPCs will no longer drop weapons or shields as separate objects, as these are never cleaned up which greatly adds to save bloating and litters the gameworld (the items will still appear to be dropped, but will access the corpse's inventory to be taken and be cleaned up with the corpse if left)