When you upgrade your crossbow you get the added ability to ignore 50% of enemy armor. I also enchanted it with soul trap and the enchantment never needs to be recharged as it doesn't run out.

I was wondering if its a bug or not. I havn't tried it with other enchantments yet.

Probably a bug. It probably didn't get fixed up to use the soul gem fused into it.

the thing is, it still soul traps and my soul gems fill up but it doesn't use up the enchantment....so YAY free soul trap enchant

ineteresting...

I was using the mace of molag bal in a dawnguard quest and it had completely out of enchantment but would still soul trap enemies.