While testing #23554 I've found that showing cube sample on high DPI screen works weirdly:

1. On startup, the cube itself is twice bigger than it should be.
2. After switching to another application and back things become even weirder: it becomes smaller, but squashed, jagged and the canvas becomes bigger than the window containing it (!) resulting in BeOS style window like this:
   

The second problem might be related to the GTK/Gnome bug, but the first one probably isn't.