I don't know, but when I close Flash CS5 (not CS4) my computer starts locking up and it's so annoying!! Does that happen to anyone else??
Do you get a crash log? If so, can you post it here?
This doesn't seem to be a crashing issue. The program seems to be designed like Windows, wherein the application quits when you close the last open window. This is incredibly annoying and completely unacceptable.