REG 5.14.2>5.15.0 Popup menu appears in primary monitor, even when main window is on secondary monitor

I'm reporting an issue that appeared in mkvtoolnix gui after the developer upgraded from Qt 5.14.2 to 5.15.0. I tried to contact him first but his reply was that he didn't change anything except upgrading Qt.

When you have the program on the secondary monitor and click on a button that should display a popup menu, it's displayed on the edge of the primary monitor.

I have attached pictures that show the correct behavior with Qt 5.14.2 and the incorrect behavior with Qt 5.15.0.