The following scenario locked up my machine:
I chose "Build Application" from the File menu. There was one file that needed
recompiling, so TPM displayed a non-modal progress dialog.
During the compile, I switched back to the Finder. While the Finder was still
the front app, the compile finished, and TPM put up the standard save dialog in
the background (i.e. behind the Finder windows).
When I switched back to TPM, the standard save dialog was completely blank, and
I couldn't get rid of it — it didn't respond to clicks, or to Esc or
Cmd-period. In the end, I had to Cmd-Option-Esc to kill off TPM.
Regards,
Robin