In Gloucester MA, COZI TV (Xfinity channel 935) is being broadcast in the wrong aspect ratio.
Comcast is getting a 16:9 signal from COZI, but they're broadcasting it as if it was a 4:3 signal. The result is that 16:9 commercials are squished to 4:3, and old native 4:3 programs (like Bionic Woman right now, for instance) are being squished to a ridiculously thin picture.
It's been like this for a couple weeks now.
I tend to watch COZI more, but now that you mention it, I have seen this issue occasionally on other SD channels as well.
A couple years ago I went through this when MEtv was being broadcast incorrectly, and I contacted the local affiliate and Comcast---Comcast said it was the local affiliates fault, and the local affilliate said it was a problem with Comcast's equipment, as I recall---but they did eventually work it out.