The issue is with the definition of that particular UI element (either the entire UI frame or the top-right compass/corner section, depending on how it's defined). Most likely when it was defined there was nothing in the window elements dds in that region, but when something new got added the definition for the element wasn't adjusted down to not include that bit.
I don't remember off the top of my head where that particular element is defined, but the fix should be to just trim it down by a pixel or two to avoid the new element.
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