Using evolution with an Exchange mailbox illustrates this well, because it's a bit slower. I move 1 message from an Exchange mailbox to a local mailbox, then start moving a second message from an Exchange mailbox to a local mailbox. I do this by dragging and dropping. If the first move completes before I have released the left mouse button for the second move, the cursor stays as the "Move" cursor, permanently. I can't use my mouse for anything else any more - for anything - clicking no longer works. The workaround is to Ctrl+Alt+F1, then login, then kill evolution, and Ctrl+Alt+F7.
Thanks for the bug report. I'm going to move this to the upstream bug tracker where I'll continue to track the problem. Please see [1] for further updates. [1] http://bugzilla.gnome.org/show_bug.cgi?id=465053