Confusion between virtual desktops and viewports
Binary package hint: compiz
There is confusion between "Virtual desktops" and "Viewports" in Compiz. Both use the workspace switcher applet, which behaves differently depending on the settings.
Virtual desktop and viewports can be set in the Compiz settings menu under General options, Desktop size. When "Number of desktops" is set to 1, the workspace switcher applet shows the number of viewports. Using the keys crtl+alt+
If I set the number of desktop to any number higher than 1, the applet suddenly shows desktops, and no longer viewports, without any indication of that change. Using the hotkeys I can still switch between viewports, however, the applet does not change because it shows desktops. Clicking on the applet to switch to another desktop is possible, and there I have a whole new set of viewports. There are no hotkeys to switch to a new desktop.
From this new desktop, I can only see the application on the viewports associated with this desktop. E.g. the window selector applet only shows windows from the new desktop, and not windows from the first desktop. These windows are 'somehow lost'.
The unclear distinction between desktops and viewports leads also to other bugs, such as #145704. It is also not possible to drag windows between viewports, but it is possible to drag them between desktops.