This might not be a valid bug since the user is expected to open the drawer by clicking its button, but I noticed that if a global drawer shows up as a menu, calling its open() function causes it to still show up as a global drawer, but in a inactive/disabled state. The expected behavior would be that the menu is opened instead.
The problem is that open() is implemented in the source QQC2 Drawer, and we can't in qml do a reimplementation that calls the stock implementation if is not a menu, as there is not a such thing as "superclass" :/