Problem with Micro-cap 12
After much searching, I noticed that other circuits didn't behave this way.  I looked at files the simulator generated that were specific to the circuit with the polar plot, and in the .cir file, I noted a section titled &quot;[Waveform]&quot;.
In it, was a line &quot;Chart Type=Polar&quot;.  There were two of these &quot;[Waveform]&quot; sections in the file, with the first line under them being &quot;Analysis=Transient&quot;, and each with a different &quot;AliasID&quot;.  I compared to the working circuits, and saw that the only difference was that the &quot;Chart Type&quot; line didn't exist in them.
After deleting the two &quot;Chart Type=Polar&quot; lines and restarting, the Transient analysis window now appears as it should.

This may have been a bug bug of some kind, or it may have to do with me fiddling with the &quot;PSS&quot; option, although I'm not sure why...I just recall this being one of the last things that I had experimented with before the unwanted behavior occurred, and that the simulator ran for much longer after the line I deleted.  I then discovered that &quot;PSS&quot; had been switched on.