결론은 비동기냐 아니냐 차이
popBackStack
Added in API level 11
void popBackStack ()
Pop the top state off the back stack. This function is asynchronous -- it enqueues the request to pop, but the action will not be performed until the application returns to its event loop.
popBackStackImmediate
Added in API level 11
boolean popBackStackImmediate (int id,
int flags)
Like popBackStack(int, int), but performs the operation immediately inside of the call. This is like calling executePendingTransactions() afterwards.
