The following applies to Lucid 10.04
It happens on my "real" computer and also in a VirtualBox VM...
(UPDATE) I just now installed Maverick 10.10 to a VM... and almost the same thing happens!
I do have keyboard control (initially) but the only way I can exit the terminal is to close it with the process still running (or Ctrl+C), and this causes the lockup (pressing Enter doesn't take it back to the prompt)
$ metacity --replace
The above command (in the terminal) causes my system to hang, every time.
The command does not return to the prompt.
The window decoration disappears (maybe because the command hasn't completed?).
The keyboard becomes non-functional, (but the mouse still works)...
However, the following commands work fine, every time.
$ (metacity --replace &) $ metacity --replace & # this works too
It may "hang" only in that I loose the keyboard, and so can't press Enter to bring it back to the prompt, (...as I have noticed is the case with some unrelated commands which don't "fully" return to the prompt, until I press Enter)
What's going on here?
My "host" OS is not new, but the VM is in mint condition (almost)... and they both exhibit this keyboard "lock-up".