In Ubuntu (including 8.10) there is a bug that does not allowmore than 7 windows to open without consequences (+ observance of the condition). The bug repeats itself if your “taskbar” is located on the right, and not below, as usual. After opening the 8th window, you can no longer interact with the panels (the Application, Places, System menus are not available and you cannot select a running application using the mouse, only Alt + Tab). The defect has been known for more than a year. See description: https://bugs.launchpad.net/ubuntu/+source/gnome-panel/+bug/187540
PS: I myself ran into this problem, it is very annoying when in the process of working I have to overload the panels.used to seeing the panel on the right, becauseI have a widescreen screen on the laptop.I solve the problem for myself through the terminal - killall gnome-panel . The Ubuntu transition experiment is still in progress.