There is an issues with window properties in tests/qml/configs/tst_configs.qml. See the code that is commented out (at the bottom). The problem is that in multi-process mode setting a window property on the server doesn't trigger a windowPropertyChanged signal on the client side. Debugging with WAYLAND_DEBUG=server showed, that the signal is sent from the server, but never processed by the client. The issue has been observed in a test case only (for instance setting a window property in the minidesk SystemUI would properly trigger a change event in an application). Note that the Wayland ping-pong does also not work in this test case.

A workaround that is also used in tests/qml/windowitem2/tst_windowitem2.qml, is to have an animation running in the SystemUI. However, another issue was observed in this case:  the notifications test would sporadically fail (once in ten runs).