After changing I get continuous transport errors and the picture/audio
breaks up. It doesn't seem to resolve within a few seconds. If I quit
live TV, Myth keeps the frontend running and tuned.
I would suspect Myth's buffering.
I would too. However, Myth is only declaring transport errors when it
sees the transport error bit in the MPEG-2 TS packet headers. So I think
buffer management in Myth must be causing overflows on the card, or
something like that. That might explain how tzap/femon report no
uncorrected errors yet I still get error-flagged packets.
There is no part in the driver or firmware that sets the error indicator
bit, that's up to the demodulator which does so in case of uncorrectable
block errors after applying the FEC.