Particle Question

I tested now a few days the particle system and it is really easy and good to use.
But i have a question about the position. If the screen scrolls, the position of the particle is fine but the angel of the particle change.
I guess it is about the rotation or something but i cant find a solution.
I used 3 particle with 3 different cloud images for this test.
In the picture you can see what i mean: left image - is if the screen scrolled left, right image - if the screen scrolled right.
Does anybody know how to fix this, so the angel is allways the same?

Umon