Not sure I've picked the right component... but anyway... Just updated to 5.9 and tried out the new Global Menu feature with LibreOffice 5.2.5.1. When choosing titlebar button, the LibreOffice application menubar is removed but no "titlebar button" appears. The menu, so far, remains inaccessible.
Also tried with Application Menu Widget. Removes menubar from LibreOffice but the widget remains blank.
Just installed 5.9.1. Checked Global Menu with LibreOffice and still no love.
*** This bug has been marked as a duplicate of bug 376232 ***