FPlatformMisc::GetScreenPixelColor() only returns black in fullscreen

I have written a color picker in C++, which is supposed to be returning the pixel-color at the current mouse position. This works fine in PIE and in the packaged version (when it is in window mode)… but as soon as I play in fullscreen mode, the function only returns a black color:

FIntPoint GlobalMousePos;
 GEngine->GameViewport->Viewport->GetMousePos(GlobalMousePos, false/*bLocalPosition*/);
 FLinearColor TintColor = FPlatformMisc::GetScreenPixelColor(GlobalMousePos);

So TintColor is always black when playing in fullscreen. What am I doing wrong?

Though it is no real solution to this problem, I used a different method to read the pixel-colors of the Texture2D with the help of the Mouse-Position minus the Texture-Position on the screen.

I’m having same issue with black values from the pixel color, i can compile, no errors report, no values comming out of the node but black (alpha is 1 so it seems to send something)

Is it a bug?