This is not a known issue....
Have you checked (and scrolled down) in every part of your Hero and DK's inventory???
Sometimes items jump over to the Hero's inventory (mostly quest items). They can also hide out of direct view... but scrolling down should reveal them.
Have you checked that its not hiding underneath something else in your inventory? Move some items around and see if it doesnt appear from behind one...
THe crystal bag in act 1 is the only one in the game.
shout if you need more help or if you cant find it...
