New stations show up on (OTA) channel list-why?

I OTA-only with my Roamio Basic. I have a directional chimney mounted antenna pointed south where all the local towers are located. I am about 85 miles from Chicago which is almost due west. Today I got a Tivo message saying they had added channels 5 and 7 which are the NBC and ABC Chicago stations. I looked at the signal strength readings and got 32 on ch 5 (not strong enough to produce a picture) and 0 for ch 7. Both these channels are in the pink range on the TV Fool plot with power readings of -85db or less. The weakest local channel is -40db.

So my question is why did Tivo add these to my channel list? This is not the first time this has happened. In fact, I've got almost as many channels on the Tivo channel list that I don't receive as channels that I do receive.