Disable_topmost is set to 1 or 2 and the taskbar is on autohide.
If you open the hidden icons in your notification area and rightclick an icon, the menu will appear behind the icon list rather than on top of it. Some rightclick menus don't appear at all. Furthermore, opened rightclick menus sometimes get stuck open even when you click elsewhere.
If you press windows key to bring up the taskbar and start menu, then click the arrow in your notification area to open the hidden icon list, the taskbar and start menu get hidden and nothing is opened.
Again bringing the taskbar up with windows key, if you click an icon in your notification area that isn't hidden, the taskbar and start menu get hidden and your notification icon gets moved into the hidden area. Even if single clicking that icon was meant to bring up the corresponding program, it isn't opened.
Customer support service by UserEcho