I have only experienced similar problems while running tor exit node, even with very restricted exit policy. Allowing exit only to port X, and unable to initiate connections to port Y (typically Y=HTTPS=443, of course X =/= Y). 

Note that those problems are not Comcast's fault, although they do point to more general problem: that people (webmasters, cloud services, ISPs) sometimes block too much and misunderstand tor, they probably wanted to block just tor exits, but end up blocking anything tor-related. 

This leads me to following idea: Educational campaign to teach relevant people about difference between middle relays and exits. My proposal for title/slogan: "Tor relays are not a threat - no reason to block them".  (Should it be "middle relays"? But it seems too long then.) EFF could be quite helpful there.