We are in the verge of solving this bug. We have already tested it happens only in intel when there are emmitters in the scene, using phisical sky with sun works well.
While we solve it (we think it will be really soon), you can always make mxcl open in emulation with Rosetta. You can do that selecting "Open using Rosetta" in the Info window of mxcl and mxcl server if you are running in network. It will work slower but at least it'll work without dots.
nachob