I put a forged receiver which says +50% condition onto my service rifle as a mod... then when I use repair kits it damages the weapon instead of repairing it.?
What is going on with that?

As the mod bring the weapon's condition to 150%, WRK would bring it back to a 100%.

All mods that raise weapon CND are bugged. Don't bother using them.

Same goes for all weapon mods that lowers weight. While they claim to lower the weapons's wight it does exactly nothing to the stats. Drop your Sniper rifle with the carbon fiber parts to see for yourself.

Well, weapon condition mods works if you repair it the normal way, so I wouldn't say no (and with Jury Rigging I can repair my Brush Gun with BB Gun).