HMX devs don't answer every question, it seems. Back when we got the six singles a few weeks ago, I asked why some of the backing vocals were removed in I Melt With You, and it was never answered, so.
Actually, it was answered in that discussion thread.
Originally Posted by Eric B
I’ve seen a few questions on the forums about “I Melt With You” and missing some of the BGVs. I originally thought they were missing too because the version I was familiar with had them. And we contacted the label about it. Turns out we have the original album version that never had those BGVs. Those BGVs were added sometime later, maybe in one of the several re-records they did.