I've seen the above behaviour for a while now and it still happens with my DVB-T tuners, Occasionally some channels (Pick, BBC ONE HD, Dave) also load with only the audio description channel, channel changing in and out always sorts it.
However when it goes wrong with my SAT>IP tuner the behaviour is slightly different - The only channels I've had problems with are those below and these go wrong frequently.
Clubland TV, Capital, Heart -> Works fine after the buffering (Clubland seems to be the hardest channel for it to tune too).
However the Bauer music channels all go rather screwy after a buffering windows - the only way to get those channels viewable again is to stop and start watching tv again.
Heat - loads with video but no audio
Kiss, Kerrang!, and Magic - load with audio but no video