I remember that thread - too bad it didn't get narrowed down to a cause. But I can't discount the possibility that "something else is in there". After all, it's a new tank with new gravel and a new HOB filter - any of these things might have been a little contaminated. I first noticed a difference in the surface tension a couple days ago, a day after I'd put the gravel in. I didn't really spend a huge amount of time rinsing it - the bag claimed it was pre-washed and all that jazz, so in theory the only thing that should have been present was a very small amount of dust.
All my water tests (Ammonia, nitrite, nitrate, pH, KH, GH, Phosphate) have appeared normal, so I'm in the same boat as Deepfathom was - no clue what's actually causing the foam.
I'm going to try removing anything on the surface of the tank, see if the bubbles come back - this might just be a film of some kind on the surface.