I'm sorry, i cant answer your question though I'm curious of this too.

My car does it quite frequently, everyone told me that its OK "its a WRX thing" or something. took my car down to the drags and both times I've hit limiter and backfired but this time a big flame came out the exhaust. everyone said that was fine too...

im not sure of the technical side of it but in my car apparently soemthing has been swapped and that it send the same amount of fuel through, and thats why. But i'm not good at this stuff.

So in all my jabble i'm looking for a more mechanical reason