There's a woman at work who does that-flushes multiple times while she's still on the toilet. The sound of flushing water is all muffledf-I have no idea why she does it.
That sort of thing's been happening since the '70s. It only happens to fat people who's ass cheeks can cover the vents under the toilet seat. Vents that are there to prevent just this sort of thing. Most aircraft even have warning labels in the toilets because of it.
She flushes before she wipes, I think. I don't stand on my toilet and look in her stall, but you can tell cus it's always so quiet in there. I don't know why, it's just weird.