SKEmitterNode bug in background

Hi,
I have a problem with the SKEmitterNode. When I put my game in pause, the emitter goes correctly on pause and stop going. But when my game goes in background (handled with the observer on UIApplication.willResignActiveNotification), and then I reopen it, the emitter is still there until I play the game. The code that is performed when the game enter in pause is the same (due to I use a state machine to handle it).
When the game is paused, I set my emitter.isPaused to true and its speed to 0.