So I've noticed that the game sometimes freezes for two seconds or so when starting or interrupting the simulation. When I quit the game later my computer shows me the "About this mac" panel which can be opened via the dropdown menu in the top left corner (Apple-symbol). This quickly led to the assumption that during these mine-freezes the mouse actually opens stuff in the background because the start-/stop button for the simulation is pretty much in the same place as the Apple-symbol. I wouldn't mind looking at the "about this mac"-panel once in a while, but one time my Mac suddenly shut down while playing. I suspect that this wasn't caused by a crash since the computer shut down properly. Also, it would take a lot to make a mac crash that hard and I didn't have any problems with the game before.
So my conclusion is that during one of these freezes I accidentaly hit the shut down button in the background, because it is accessed via the same drop down menu.
I've attached a screenshot of this menu to make clear what the problem is.


My system specs:
OS: 10.6.9 Snow Leopard
CPU: 2,4 GHz Intel Dual Core
RAM: 4GB
Video: 256MB shared ram (nvidia gpu)
res: 1280x800
MacBook from 2008