I mass subscribed several testing addresses to a newsletter with the mymail+1@gmail.com, mymail+2@gmail.com, etc. pattern.
Newsletters get delivered OK, but when I click the direct unsub link in the footer, the address is not removed from the newsletter's subscriber list. Same newsletter issue has no problems with mymail@gmail.com direct unsubscribe link.

Relevant infos:
http://support.google.com/mail/bin/answer.py?answer=12096
http://tools.ietf.org/html/rfc2822