Now that I have gone through the Comodo forum thread I recall that this is an issue that has been outstanding for some time with Comodo personal firewall and is NOT a new issue between avast and Comodo.
The new information that has come forward is that the "Skip loopback TCP connections" option in the Comodo firewall apparently overcomes the problems that have affected the users of the avast Webshield as reported in these forums. I cannot speak to what, if any, exposure selecting that option means to a Comodo firewall user.
I suspect that we will need to leave it to the technical folks of Alwil and Comodo working together to provide a final resolution.