I've fiddled with the settings to auto-remove things from my bars, and they don't seem to work right. During combat, when I click to cast or use an item, it randomly disappears from my bar without activating. I have to open up the inventory or spells menu and re-add that item to my bar before I can cast/use. It only happens to me in combat, and it's frustrating. I think that's what the OP is getting at. Having the auto-removed checked or unchecked has no effect on this glitch. The only thing that keeps stuff where you put it is pad-locking the bars, and the bars are always unlocked again at the start of a new combat. It's a real pain to train yourself to first lock your bars before taking any other actions on each character just to make sure they stay put when you need them.