To get the mail-followup-to header to work in Mutt you must use the subscribe command and not the lists command to indicate which mailing lists your on. If you use lists then Mutt thinks you are not on the list and adds your address to the mail-followup-to hedaer.
It took me a while to figure this out even though it is documented. I think I had an old config file that used lists before subscribe even existed. Making this error defeats the purpose of mail-followup-to and I suspect other people have made the same error. Perhaps the Mutt manual should be updated to make this more clear. Neil