And a bug unknown to me. Early on, I thought double-clicking an item was the only way to transfer an item from one container to another, or dragging it across which is subject to dropping it.
Somewhere (probably here), I leaned to shift-click the item for a transfer and have been using that ever since. The only exception is when I transfer armor from a thrall’s inventory to his equip slot. Does it happen then?
Regardless of your answer, let’s go to the basics.
Could you verify your local files through steam? I wrote a short guide here if you have not done that before.
Regards
jim