It would have been better left unsaid, but it is not a major gaff.
Why? The Obamanites brought up the tax release issue. If Mitt had any balls he would be shoving the release of the birth and school records up Obama's a$$ daily.
But Mitt is too polite. Should he get nominated look for him to pull a McLaim and get his ass kicked. Sometimes you just have to call a spade a spade ... no pun intended.