Well, this was just a symptom of a much larger problem. /sda1 was 100% full. mythtvfrontend.log was absolutely huge filled with this:
2008-12-29 10:59:57.397 NVP: Prebuffer wait timed out 10 times.
2008-12-29 10:59:58.847 NVP: Prebuffer wait timed out 10 times.
2008-12-29 11:00:00.314 NVP: Prebuffer wait timed out 10 times.
2008-12-29 11:00:01.830 NVP: Prebuffer wait timed out 10 times.
2008-12-29 11:00:02.224 LiveTV forcing JumpTo 1
2008-12-29 11:00:02.239 LiveTV forcing JumpTo 1
2008-12-29 11:00:02.240 LiveTV forcing JumpTo 1
2008-12-29 11:00:02.240 LiveTV forcing JumpTo 1
2008-12-29 11:00:02.240 LiveTV forcing JumpTo 1
2008-12-29 11:00:02.240 LiveTV forcing JumpTo 1
2008-12-29 11:00:02.240 LiveTV forcing JumpTo 1
And that repeated a few millions times.