thats normal. Some channels are adding subchannels on digital TV (just like they do with FTA)
example
analog takes up the whole bandwidth
digital they can split it up and give X amount of bandwidth to one channel and X amount to another
I have a Dish811 receiver that can get digital channels but my TV isn't HD. Here in Minneapolis we have the following on subchannels
5 is the ABC station. 5-1 is ABC and 5-2 is 24 hour weather & news
9 is Fox. 9-1 is HD (when available) and 9-2 is Standard def
11 is NBC. 11-1 is HD (when available) and 11-2 is weather +
17 is PBS. They have 5 stations. 17-1 is PBS 2 (the main PBS in town), 17-2 is 17, 17-3 is TPT Kids (like the old PBSKids), 17-4 is PBS Create and 17-5 is 24/7 weather radar
23 is WB (now CW). 23-1 is WB and 23-2 is the Tube (main reason I have it)
so the box allows you to get more channels (depedning on your area and what stations your local affiliates shows).
In Duluth, CW is on the CBS subchannel (3-2) and MyTV is on the NBC subchannel (6-2)