explorer: tray icons sometimes disappear when using the start menu

When opening the start menu and moving the selection around, the tray icons disappear.
This doesn't happen always, so one may have to try a bit around. They reappear after different actions,
for example when closing the start menu and clicking the taskbar or when clicking on the tray area
(clicking the tray area seems to work every time, in contrast to clicking the taskbar for examle).