Motion artifacts

I think not, it seems to be a problem of the latest Flash Player update. It appears on my both PCs exactly after the update one by one. I hope with the next Flash Player update it will be fixed!

Beckhusen, I did not touch the 5D2 neither the cards since I posted the question.
I am processing amazing video from the GoPro Hero 3+ and surprize!
The artifacts are also in protuned clips but not in the original files.
I still have to take the card from the 5D2 and watch the original files on another computer.
I will report.
I am updating all my video programs, codecs, Java, Flash etc.

Don, I have seen this problem as well not only on my clips but also on yours.
The problem disappeared after making the above update.

Verdict:
After replacing and updating all the programs drivers and cards, still I had to render my clips again and again because of the artifacts. I got fed up and took the computer to the repair shop. One of the RAMs was malfunctioning. It was replaced under the warranty.
The computer was reborn and my life went back to normal.

That means, a PC RAM failure caused this problems??? Crazy, i never would imagine that this can happen and can belong together. Thumbs up for you and congratulation that you got it!

pc ram failure made it happen consistently at the exact same spot?

No, every time different spot. I had to render or save as several times until one version had no artifacts.
Just copying files from card to pc created artifacts. I had to make two copies from new files until solution was found.