These other users cannot unmount the removable media. Yet they also don't see the mounted disk images. The OS simply complains the "disk is in use" when you try to unmount the removable media. So there is no clue offered as to what the problem is. The "solution" or lack of one, is to always unmount disk images before your log out.
I can't decide if this is a feature or a bug. On the one hand, it's nice in the sense that when the user logs back in, all his mounted images are still there where he left them. On the other hand, if you have several users, it's a giant hassle to undo this problem when you run into it. Indeed, only someone who knows all the passwords can undo this properly (without resorting to dangerous terminal commands or shutting down the computer). There probably ought to be a preference switch for this behaviour.

