Run attached QML files:
qml compositor.qml &
and
QT_WAYLAND_DISABLE_WINDOWDECORATION=1 qml client.qml -platform wayland
Use mouse buttons on the orange and blue rectangle like so:

1. Press left
2. Press Right
3. Release Right
4. Release Left

The order of 3. and 4. does not matter. Expected result is that a release event is sent. This is the case for the orange rectangle, however not for the blue Wayland SurfaceItem. If steps 2. and 3. are omitted, it works as expected also for the SurfaceItem.

It is even worse, when the MouseArea is not a child of ShellSurfaceItem (needs "anchors.fill: ssi"). After 1. and 2. no mouse events are sent any more at all.