Steps to reproduce:
Now, as a programmer myself, I realize the implication here, but it seems to me that there is some kind of asynchronous thread processing the effect and by trying to apply another effect at the same time it tries to access the same object as data at the same time; thereby, creating the collision.
If I'm not mistaken, care needs to be taken with the thread pool to lock-out other threads from accessing the same object until it's done.
Granted, users should probably not do this type of action, but I did find a scenario in which it was useful. That said, PP should definitely not crash under any circumstances and I hope I've provided not only enough information, but a resolution as well.
Furthermore, I would be willing to bet that this "bug" produces crashes in other, less ridiculous, circumstances and that by fixing this bug, you might also fix other bugs that were hard to trace, previous to now.
I responded to your other thread :-)