This is supposed to be fixed (at least for regular tuners) in the 0.16 release. I filed a bug on the MythTV bugzilla http://www.mythtv.org/bugs/ about the issue and it was resolved pretty quickly. The problem seems to have been a generic one where the backend gave up on a bad channel and the front end didn't know how to handle it, so I'm guessing it's fixed for all tuner types.