This manifests itself as flakiness in tst_xdgshell::popup. The easiest way to reproduce, is to run the test multiple times in quick succession, i.e.:
It crashes because when we flush old pointer events, we dereference a raw QWaylandWindow pointer which may be dangling.
This is a regression in 5.14, as 5.13 didn't have that pointer, and didn't handle wl_pointer.frame events.