And I too am having the same issues. I returned my new Mac Pro; purchased a second. Same rendering issues. By rendering from AME as "software only," the glitches go away, but so does my time. The difference between rendering a 15 minute show in Open CL vs software only on my new Mac Pro is ten minutes and two hours. When tasked with producing three 15-minute shows, the workday is consumed. Performing this job on the newest edition of Premiere Pro -- CC 2014 -- produces the same unusable results.
I have been using a variety of media, including ProRes 422 HQ, regular ProRes, DVCPRO. All negative results.
Tom