When the difficulty of "improved mobs" come to a high number, when you give a villager any weapon, this item has a high chance to be enchanted, Then kill the guard can take the item back, repeat the operation can be a disaster.
If there is a chance to keep the nbt data of the item player give, could be better to give compat to other mods.

Improved Mobs should have a black list to mitigate against this.

EDIT: upon some further investigation I found out they don't unless I missed something, please go suggest this to the creator of that mod.