I confirmed this issue on the following configurations:
– OSX 10.9, Steam version “Jan 2014″, iMac 24” 2009
– OSX 10.9, Steam version “Aug 28 2014″, iMac 24” 2009
– OSX 10.10, Steam version “Aug 28 2014″, iMac 27” 2014
I get the same error on all three configurations.