northboy
I think this is what happens when they are in the process of changing the broadcast frequency and for a period of time the channel is available twice. The second occurrence is given a number of 800+. If you retune in a month's time, it should disappear.
This happened to me too. The channels that 'disappeared' were at the end of the channel list with new high channel numbers. I re-tuned and all went back to their right place and a new channel also appeared. Don't panic - it is curable.