To reproduce this in the HelloWorld example, add
Desktop::getInstance().setGlobalScaleFactor (2.0); to e.g. the constructor of the MainComponent.
-> The DocumentWindow can only be moved such that its (x,y) stays in the upper left quarter of the screen.
setUsingNativeTitleBar (true); gets added to the constructor of HelloWorldWindow, the DocumentWindow can be moved to any position on the screen, but it will snap back to a position where (x,y) is within the upper left quarter of the screen as soon as the mouse releases the window.
I suspect this is caused by the ComponentBoundsConstrainer of the ResizableWindow and the fact that monitor sizes also get scaled by
Desktop::setGlobalScaleFactor(). This happens at least on OS X.