I had the same problem. Ziggo did move History HD to another stream and after a rescan History HD is added to the channel list, but MediaPortal doesn't remove the old channel and mapped the new channel to the old channel.
When you go to the TV Channel list in the TV Server and remove History HD (Has twice 'Ziggo' as provider) and do a rescan the problem is resolved. This is also valid for some other channels with double provider entries.
gr8 , checked if this is already on the buglist.. and it is.. (or looks like the same problem anyway)
0002889: Combined channels from two sources appear twice in channel group listing - MediaPortal Bugtracker
so should be fixed in RC3 ! thanks for the quick reply..