Comment 38 for bug 1200829

If a client (normally a reparenting WM) sets a passive button grab and it is triggered when the pointer is above another client's window (eg. a WM-managed window), crossing events will be rightfully generated, however XI2 crossing events in the second client don't contain the expected mode, XINotifyPassiveGrab/Ungrab would be appropriate here, but XINotifyGrab/Ungrab are used instead.