WinTV HVR-850 again not working

I tried signing up for schedulesdirect.org and in the process of doing so had to rejig the MythTV setup to use these new listings.  While doing so, MythTV had me rescan for channels which now no longer appear.

I'm getting "Timed out, no signal" on channels that (rightfully) have no signal, but "Timed out, no channels" on those that previously worked.  I tried upping the timeouts to 10 & 12 seconds, but to no avail.  The machine hasn't been restarted, nor the device removed since it was working last.  There's no reason that I can see for MythTV to no longer be able to acquire these channels.

This is frustrating.  If you haven't already, DO NOT purchase the HVR-850 (or HVR-950 variant).  Get an HDHomeRun or similar and be happier.