Maximize button of a window is disabled when its maximumSize is not set to QWIDGETSIZE_MAX x QWIDGETSIZE_MAX

QWIDGETSIZE_MAX = 16777215 (0xFFFFFF)

Reproducible on Windows with the following code:

#include <QtGui>

int main(int argc, char **argv)
{
QApplication app(argc, argv);
QWidget widget;
widget.setMaximumSize(3000, 3000);
widget.show();
return app.exec();
}