Basically the mouse pointer disappears and it becomes impossible to pick anything up because you can't aim at anything, and makes it almost impossible just to log out of the game. I've noticed it happens a lot after elite kills. Not sure if that helps nail down the problem. But I'm pretty sure that is what it relates to as every time it happens i spend 15 mins trying to pick up rares without a mouse cursor.
If anyone knows any workarounds, please offer them.