Ok I will expand this bug report as it happened to me again and this time i could analyse the problem closelly.
I had a bastard sword on my bag. Tried to add it to a magical bag that didnt have space for it.
Instead of the bastard sword returning to my bag or going to the ground, it just disapeared.
As I saw it disapear i tried to find it in the ground or close by...nothing.
Nowhere in my inventory as well.
Nowhere in any of the magic bags i possess.
Now i am afraid this sword might be counting with my weigth even though its not in my inventory....cant be dropped...cant be moved.