The problem didn't exist in the 5.6 beta, but is here as of today, January 22, 2016.
If you move a window from one screen to another with a different device pixel ratio, the widgets are not resized properly IF there is a QOpenGLWidget in the hierarchy.
Again, some change between the beta and today has caused this.
You can see in the attached images how the window is resized for the retina display, but the widgets in it are not.
|For Gerrit Dashboard: QTBUG-50613|
|147089,2||Fix tlw source rect transformation for backingstore blit.||5.6||qt/qtbase||Status: MERGED||+2||0|