I have a Toshiba Satellite Pro L500 laptop on which I installed the beta of Ubuntu 11.04. Things seems to work smoothly at the moment, but with one niggle.

I have an external monitor connected to my laptop, and can manage to have a dual-screen configuration, and I am able to move the mouse from one screen to another correctly; however, the menus, status bars and window icons remain stubbornly only on the laptop screen. This is happening with Unity as well as Gnome.

If I disable the laptop screen with grandr (the Gnome GUI for xrandr) they do migrate on the external screen, but they swoosh back to the laptop if I reactivate it. Trying to alter the layout with grandr or using xrandr with the --right-of option from the command line do not change anything good. I randomly get the laptop screen to become half black.

Incidentally, something like it used to happen with Fedora 12 (I think) some months ago.

Any suggestions? If more data is needed, what info should I provide? Logs, configuration files?

What if you try
Replacing $externalscreen with the name that xrandr gives to your external monitor.

Sorry for the late reply, I was only able to test it today. Anyway, the suggested line works, but random areas of the screens become black when I issue the command, sometimes on the laptop and sometimes on the external screen.

Could be the video driver. What is the video card and what driver are you using for it?