Particles 'Pausing' and then resuming when back on screen

Hi
I am using the Unity Pro 4.0 Beta version, and I have noticed a ver peculiar behavior in the particle systems: if they are not played in full while on screen, they will pause, and then once they are on screen again, they will resume playing. This is not the effect that I want, and if It is a part of the particle system now, How do you turn it off?
Thanks in advance!

This effect is als
o present on the oficial 4.0 release. Any clues?

Go to Edit->Project Settings->Player.
Make sure “Run in background” is checked.