Ask HN: Pixelated graphics on MacBook Pro caused by defunct trackpad/keyboard?

Screenshot: http://imgur.com/wAAyHoV

After getting a replacement logic board from Apple for my 2011 MacBook Pro 15", I have been having extremely pixelated graphics while running a standard benchmarking test (Unigine Valley). See the screenshot to get an idea. The trackpad and keyboard of the laptop are (have been) defunct.

Apple support first suggested it could be a faulty RAM, so I bought new memory but it didn't solve the problem; then they suggested a new install of the OS, and later a clean install of the latest OS, did that and still no result. Now they suggest the pixelated graphics could be due to the keyboard and trackpad not working, and that I should get those replaced out-of-warranty. Apparently, this is the feedback coming from their engineers, via tech support.

The MacBook Pro is running stock OS and it works fine. The benchmarking tool works fine on other MacBook Pros. This problem with the benchmarking test is after the repair/replacement of the logic board, so I think it is more likely that the replaced logic board is the culprit.

I am not an expert but I find it hard to believe that defunct (connecting cable clipped) trackpads and keyboards could be the cause of pixelated graphics. Is there any technical reason that could be the case - screen graphics are pixelated because of a defunct trackpad/keyboard??

Hopefully some of the engineers around here can throw some light on this..