[Reg 5.15.17->5.15.18] QMenu cannot be closed in a Quick scene

Reproducer attached. By clicking at the MouseArea the singleton defined in C++ will pop up a QMenu. But clicking somewhere else isn't going to close that menu.

Only reproducible on Linux (tried Windows, and not reproducible). Only reproducible with 5.15.18 (6.x is all good). But since it is a regression, it should be fixed.