Obligatory Followup Post:

This loophole has now been plugged. It worked early last week for the Come Fly With Me goal, but today my attempt to complete the Boston goal, to get double credit for one song on the Grunge scavenger goal, and to get double credit for one song on the Pearl Jam goal all came up empty - star count or song count did not increment a second time when I played the same song in Blitz after RB3, nor in RB3 after Blitz.