Hey there! Are you using 4.15? I just dug through the vapor particle system, and I honestly do not know why the rotation is following the camera. In that particle system I have the Screen Alignment set to “PSA Away from Center.” I have gone through the other options and it seems for all of them in 4.15 the particles still rotate with my camera when they should not. I do not know if I am forgetting something, or if maybe they changed something in 4.15. Here is a screen shot of that setting if you want to mess with it on your end to see if you get different results. I also changed it to a normal emitter from a GPU system just in case they changed the way GPU particles work, but it did not fix this.
