I've been using IDEA on OSX for around 9 months now, and with the recent support for full-screen support I've encountered a few issues. It seems the issue is that whenever the application is in full-screen mode, and a dialog is opened (eg. Settings), occasionaly the dialog is not opened in the same screen space. When these dialogs are modal (like the settings dialog), you can't actually access them in the other screen space as when you select them, you are automatically taken back the owner of the dialog. I've seen this issue happen with other dialogs too, such as the conflict window for SVN. I haven't found a way to reliably reproduce this, but it happens quite often (on a daily basis for me).