I have been trying to work with Comcast to figure this out. Now that it is also happening to a gmail user, maybe the issue is with GoDaddy?
Sorry to hear of the trouble you've been having with the email forwarding. By any chance, was there any bounce or other error message encountered from the Comcast or Gmail account that was trying to send to the distro-list address? If you have reason to believe the issue is on the GoDaddy side, our support teams are going to need this information if you call or chat in about the matter. You can also submit a copy of the bounce for our email teams to look into through this form.