Hey there, David!
I had a peek at the form and the list that I'm being added to. It appears that the forms for the list have a different subject line and heading in the actual "welcome" and "confirmation" emails. This can be adjusted from the MailChimp side by going to the list you want them to be added to and clicking on "forms". From there, you'll be able to edit each part of the confirmation process to ensure that the list provided in the subject line matches the actual list people are added to! :)
How do I customize each part of the confirmation process?: http://eepurl.com/gOGY
Because you're using the "Advanced forms", the process will be slightly different, but this should give you the gist!