NSNumber with if statement in different situations

I know to check whether 2 NSNumbers are the same you need to use ([A isEqualToNumber:B]) instead of (A == B) unlike NSIntegers.

However, I have just realized (A == B) works just fine in simulator and I'd like to know why.

The stranger thing is that on device, (A == B) STILL WORKS as long as the numbers are below 13 and from 13 it will stop working then only ([A isEqualToNumber:B]) works but that is if they're bigger than 12 otherwise (A == B) can still be used.

Why's that??