Dialogs behavior on Wayland is wrong (modal/modaless)

Using the attached sample application which performs one simple thing.

1. Create the main window with the button

2. The button opens up modaless dialog.

3. Modaless dialog has another button to open a modal dialog.

First sanity check on Qt5.12.2 on X11 Shows that I can switch between main and modaless dialog. And every interaction is stopped when I open a modal dialog.

A second test on Qt5.12.2 with Qt compositor (Wayland) on x64 platform. A modal dialog is ignored (except that I can not click the buttons) other Dialogs can be activated and hides the modal dialog.

The third test with Qt5.12.5 using Weston as a compositor on arm Linux shows the same behavior as above.

The fourth test with Qt compositor on the arm Linux is much different. For some reason all dialogs are frameless, ther are no frames with a close button. But also every dialog is blocking. Cant activate nor bring any underlying dialogs regardless of modalness.

I think that Qt doesn't handle them right stacking order with Wayland as the same behavior can be shown on qt compositor and on Weston.SampleModal.tgz