A.) It has become clogged or
B.) You're having a Double Stacking contest
DOOKIE: NO! What'd you do man?
J: Well I tried to flush it, but it just spun around a bit. There was no way I was gonna make it home without squirting all over myself.
DOOKIE: Dude, tell me you didn't....
J: Yep, I just Double Stacked it.
The dealer claims that the pill is "double stacked", ie contains twice the amount of MDMA and sells it for a higher price.
It's a lie used to shift more pills and pull in more profit.
Double stacked pills often are slightly larger, because they contain twice the amount of filler.