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Apple’s recent OS X Mavericks 10.9.3 update is causing even more headaches for users of the latest Mac Pro line. Last week, we reported that 10.9.3 incompatibilities are the source of GPU issues with professional video editing programs. Now, multiple threads on Apple’s support forums are indicating issues with 10.9.3 Mac Pros and multiple external monitors. The issue causes users with several monitors to only see a portion of their monitors functioning.

As one user explains:

I have three 30″ displays, but after the 10.9.3 update, only 2 of them work at a time. Is this a known issue? Can I downgrade to 10.9.2 to get the use of my other display back? It was working just fine on my Mac Pro with 10.9.2.

And several users corroborate:

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While the several-thousand dollar Mac Pro improperly utilizing external monitors in professional work environment is a serious problem, there is some good news to report. According to one poster who submitted a bug report to Apple, the Cupertino-based company appears to be aware of and investigation the issue:

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Some users are also reporting some solutions for the problem. Some users say that re-installing the 10.9.3 Combo Update is helpful. Users are also recommending combining that re-install with a PRAM reset. Lastly, one user suggests installing the GPU driver files from the preceding 10.9.2. Apple is already internally testing OS X 10.9.4, so hopefully that update has a definitive fix for these Mac Pro GPU problems.