@Ayy 2016-08-17 16:18:360 ♡
I think it happened around the time the hips popped out.

Honestly I think that page (V1P12) would benefit a lot from being redone. It has a clashing art style compared to the rest of the comic, misses out on an opportunity to show her thighs and ass coming in, and his pants somehow manage to stay on despite having just shrunk dramatically and then suddenly start slipping off after the hips expanded. They should've been around the knees almost immediately IMO.