It appears there may be a problem with multiple active GPUs and Mountain Lion. http://reviews.cnet.com/8301-13727_...xperiencing-random-log-outs-in-mountain-lion/ The defects appears to go away if stop using monitors so that only one GPU is in video output service at a time. Sure looks like Apple QA set-up is either lax or unimaginative. Lax if didn't catch this in testing. But more likely unimaginative, skips testing completely the BTO configuration that has two graphics card. FCPX choking on the app spread over multiple GPUs seems indicative that it is the latter above.