Again (not for the first time): "background vocals" and "background singer" does NOT mean those vocals are always in the background or the singer is limited to this. Feel free to look up proper definitions for the term.
"Too bad" is mixed 2 times in the foreground, it is exactly the same voice as in the background later. On the earlier mixes this can be recognized easily, on the leaked version and the album version it appears to be boosted and has a doubler effect on it (the 2 instances it's in the foreground).
On the remix you can also hear the Porte vocals more prominently.
Listen to this, first is what you guys call "lead" (because it's in the FOREGROUND) which is James Porte's backing vocals nonetheless, 2nd is James Porte again (in the background).
It's both the same voice and it IS James Porte - as a matter of fact. (I can prove this in court.)
PorteFORG_and_BACKG
Now enough of this pointless discussion. Some people got the proper info and that's all I care about for now.