Comcast router software completely BLOWS. And I mean that. Laden with bugs, utter crap. I just got a new "gateway" from them, a Arris TG862 and it was pretty much completely unusable until they put it into bridge mode. I would get pages that would not load (static DNCP), pages that said features were disabled (dynamic DNS), etc.
I got on chat with support and they put it into bridge mode. The support guy told me I would have to get them to put it back into router mode if I ever desired (I don't)
The good news is that the thing is crazy fast, and I mean > 120 mbit/sec incoming and > 20mbit/sec outgoing. Yee-haw.