If a window is bigger than the monitor height it should be positioned so that the top of the window is aligned with the top of the display. This is how it used to be with 4.7.4. For 4.8.0 (and 4.7.5) the positioning has changed so that the bottom of the window is aligned with the bottom of the screen. If a window has a title bar one can't see that now.
The issue is easy to reproduce just by creating a QMainWindow with the height bigger than the display height.
This issue was introduced with the fix for https://bugreports.qt-project.org/browse/QTBUG-10589 (SHA c592b71d266a8f7a9bbf330fb3cbca168dbe1bfc).