MythTV lets you watch TV directly, with the ability to pause shows (say, while you are either preparing a beverage for consumption or, ahem, recycling one already consumed). You can tune up and down with arrow keys on your remote and select a channel. MythTV superimposes on the screen information about each channel (id/call sign, current program, signal strength, ...) as you tune around. Tuning displays only channels known to the electronic program guide that you configured, in effect skipping channels you do not have ... usually ...
In my case, MythTV would let me scroll to channel 16 (which it labeled TBS) or 15 (WGNAMER), but when I selected either one the tuner would crash, taking me back to the MythTV front-end interface.
I get my TV via cable from Comcast, although I'm not sure that's entirely pertinent here. I subscribe to Schedules Direct (henceforth "SD") to get EPG data, which I feed both to MythTV and to Freeguide, running on a different PC, so that I can plan my week's viewing. SD lets me setup and edit multiple lineups, and it knows the Comcast lineup for my area. To reduce the amount of data downloaded each time I grab listings, I edited out (disabled) most of the available channels, since I pretty much never watch them, and certainly never record them. (If I do want to watch one, the Comcast cable box will still list it.)
I'm pretty sure that, at one time, WGN and TBS really were on channels 15 and 16 respectively, and I had them enabled (on my active channel list) at SD. Somewhere along the line I disabled them at SD, and somewhere along the line Comcast moved them to channels 95 and 66 respectively. Apparently, though, the old numbers somehow got "stuck" in the channel lists of both Freeguide and the built in channel "grabber" in MythTV. So when I logged into the SD web site to inspect my channel lineup, the correct channel numbers were listed (and marked as disabled), but when I looked in Freeguide or (gulp) tuned manually in MythTV, the old channel numbers were there.
Reloading the EPG data did not good on either MythTV or Freeguide until I edited my SD lineup and re-enabled both WGNAMER and TBS. After doing that, I reloaded the listings in Freeguide (which now showed the correct channel numbers) and then reloaded the listings in MythTV. I'm not sure it was necessary, but just to be safe I opened a terminal on the Mythbuntu box and did the reload manually, running 'mythfilldatabase --do-channel-updates' to ensure that channel numbers, as well as program content, were updated. Then I went into the MythTV front end, selected 'Watch TV', and verified that the correct channel numbers were displayed.
Apparently it required an edit of the channel lineup at SD to get things unstuck.