@chrissam: Hmm, I must confess I am at a loss, and since I dont have OSX, it is difficult for me to debug. But if you're willing, I have a few ideas. Checkout the svn version and in the file libprs500/gui/main.py line 523 change end_session=False to end_session=True
Instructions on checking out the svn version are at
https://libprs500.kovidgoyal.net/wiki/Development