Default [Q] "Square pattern" during video playback

Here's a strange problem on my SM-P605 (Stock ROM):
This square pattern during video playback only appears when I use hardware accelarated playback (e.g. Samsung stock video player).
When I try to make a screenshot there are still there. And if I move about when the picture ist zoomed in, the pattern is moving relative to the fingers, so it not physically related to the screen (EDIT: They are also visible during the video playback and therefore not related to the JPEG export of the screenshot ).
When I view the screenie on my computer however no trace of the square. Therefore I only have the evidence of the handycam.
This is of ocurse heavely zoomed in for demonstration, but it is visible to the naked eye quite cleary especially on cartoons and quite annoying
Does anybody else here have these problems and/or does know a fix? Or should I ask Samsung technical service?
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