Yup still having the same problem here in macOS, and for a DocumentWindow that I definitely don’t want to allow to be maximized.
Calling this in the DocumentWindow constructor still results in a window with the maximize button in the title-bar:
setTitleBarButtonsRequired (0, true);
Additionally, the maximiseButtonPressed callback is being ignored (as reported here as well) - so I’m not able to disable the maximize action.