mapFromGlobal gives wrong result for QGLWidget inside a QMdiArea

When having multiple QGLWidgets inside a QMdiArea, only the first one does map the global event position (or the cursor position) to local widget coordinates correctly (ie. mapFromGlobal() gives correct result). All the other QGLWidget give wrong results.

BTW, as far as i understand, the QGLWidget does not show up correctly.

Using any other Widget, in particular a QOpenGLWidget behaves correctly.

Run the attached project, and move the mouse above the widgets. The mouse position gets displayed in the bottom frame.

I forgot to mention that there is no issue with Qt 5.9.4.