Glad you figured it out, and glad you posted as many details as you did.
Part of the issue seems to be that it sounds like you’re rendering part of the time in particleIllusion itself, and part of the time in pIRender. I suggest you maximize particleIlusion before you render, so it won’t need to use pIRender. pIllusion will first maximize the stage window to try to fit your output size. If it still can’t fit it, it calls pIRender.
I’m not saying that I think pIRender is bad, but we’ve only recently added hardware acceleration to pIRender, and there may be issues there (especially when using older drivers).
So render in pIllusion itself whenever possible for the least amount of pain.
Alan.
http://www.wondertouch.com