OK, had a major bug with MoI and OSX Mavericks.

I was screen sharing with Skype to show a friend about MoI just now. Used my older 27" iMac as a screen to my Macbook Pro Retina.

First I used the latest "MoI v3 beta Aug-1-2013" and everything froze. My computer logged out and when I logged back in again, the beta was not possible to open again.

Then I used the "MoI v2.52" version. And my whole computer froze again, but I was still able to speak to my friend over Skype.
Forced to restart the computer.

UPDATE: Seems to be something with Skype. Tried opening it with same setup, but without Skype running screen share. Works fine. Could open the Beta again too.