Ok recreated this loads of times now, I have tested with all types of items of all stat types, any weapon, armor or jewellery exotic and ascended, if you drag any item directly from hero panel window directly to any EMPTY bank slot the game will crash with serious error.
Any item drag, from hero panel to empty bank slot = serious error crash, tested this with all types of items from hero panel and was able to recreate the crash many many times exactly the same way.
Hope that info helps in fixing it. Cheers.