For most users this has been resolved.
Perhaps check the comments in this thread to see if the solutions there work;viewtopic.php?f=84&t=25851
Matching game resolution to screen resolution is the main way to resolve it, but one other potential issue was recently identified;
George Geczy wrote:
Hmmmm.... although we haven't had any other reports of this yet, it sounds like it could be an issue with the Mac Retina displays. Since these are 'high dpi' displays they might, in the latest builds, have a different way of handling this. We don't have a Retina Mac here at the studio so this is hard to test.
If there is some sort of 'Retina adjustment' being enforced to compensate for the high DPI, then you would see the actual game resolution run at half the vertical and horizontal pixel size - so a 2880x1800 Retina display would operate as a 1440x900 resolution.
We specifically turn off this pixel reduction on Windows system, I'll have to look into making this more automated on the Mac. However, your solution (using the effective 1440x900 setting) is the solution.