[REG 5.6.0->5.6.1] macOS: addMenu() doesn't work after clear() for a parent-less QMenuBar

QMenuBar::addMenu() call after QMenuBar::clear() does not add the menu for a parent-less menu bar.

The attached file contains simple example. After press the button the menu bar becomes hidden with 5.6.1 and 5.6.2_442. This code works correctly with 5.6.0.