Particle System Flickering

Hey there:

What I want to do is making a burst of particles via Code for a specific time.
After that amount of time, I want to stop the particle system and let it return to its usual behavior.
I use the following Code to end the burst:

Code (JavaScript):

1. function fadeStream(){
2.     Debug.Log(particleSystem.emissionRate);
3.     var tmpTime:float=0;
4.     var oldRate:float=1000000;       //to exit the function, if a new boost is started during the fade
5.     while(particleSystem.emissionRate>1){
6.         if(particleSystem.emissionRate>oldRate){
7.             internSoftOff=true;
8.             return;
9.         }
10.         particleSystem.emissionRate=particleSystem.emissionRate*Mathf.Exp(-2*tmpTime)+1;
11.         tmpTime+=Time.deltaTime;
12.         oldRate=particleSystem.emissionRate;
13.      
14.  
15.      
16.     yield;
17.  
18.     }
19.     internSoftOff=true;
20.     particleSystem.startLifetime=baseLifeTime;
21.     particleSystem.startSpeed=baseSpeed;
22. }

When the boost ends, no new particles are emitted, as intended:

The problem is: The already emitted particles do not fade out smoothly as configured in the particle system. During the boost everything behaves right, but about 1/3 second after the emission stops, the "old" particles just disappear, sometimes they even flicker back for a frame...

Hope you have an idea and thanks in advance!

Sincerely Vorthos


EDIT: Seems the problem does not occur, when the particleEmission is not set near 0 at the end...