Mac OS X 10.8.3 - Pixinsight 1.8 RC6: When closing multiple windows individually (I had about eight open, most were images created from previews) Pix crashed. I "think" it was a preview (not an image from a preview) that was being closed when the app crashed. That said, I had successfully closed these same types of windows in RC6 without any adverse effects. This also occured after a very CPU intensive MorpologicalTransformation process.
John
P.S. Don't know if this was supposed to be addressed in this release, but Printer Setup also causes a crash.