Oh wait, KB46758 suggest that it is "locking up" because the tag browser is opening off screen. I ran into a similar problem years ago when switching between dual/single monitors. Of course, I'm sure there are other ways to cause it.
You can tell if this is the problem by clicking the ellipse (...), then press escape on the keyboard. If it appears to no longer be "locked up" then it was opening, just off the screen somewhere.
The KB gives a few solutions to get the window back if that is in fact the problem.