A bit more info for you to pass on Impact.
I use Websceduler for most recording on an XP machine, for the last 2 weeks I have set up to record 24 Ch 7 Wednesday nights both on SD and HD channel, just after 24 has finished on Ch7 (23:34:19 to be precise) both weeks the HD capture has failed for no apparent reason. SD sails along fine and stops at correct time. According to the capture engine there is no data but signal strength is OK.
Now for the link to Vista, I set up a record of 24 HD only on MCE, Guide was fine when I put the machine in standby. It did as it was told woke up recorded for 90 minutes and shutdown. When I started the MCE this morning the Guide was messed up on Ch7. Looking at the recorded show there is a small stutter at 21:34 which I reckon is Ch7 doing something and bang there goes the guide.
Not much to go on but I am pretty sure you have watching or recording the channel for the Guide to mess up. For example I hardly ever watch SBS live and have only seen one corruption and that was after a live session.
rgds Damon