Comment 40 for bug 311748

Thanks, that's interesting! I think this is a bug "in the graphics card".The drivers have to work around this. Could you please open an upsteam bug report, in order to go sure that it gets fixed in the driver?

Unfortunately there are two drivers for your graphics chip.
On driver is called radeon, the other one is called "radeonhd". Please test also with that driver, which of the options is needed, as described here:
http://www.x.org/wiki/radeonhd
(in section "10.5. My monitor isn't detected").

Here you can create a new bug report upstream (You have to register there first, though) :
https://bugs.freedesktop.org/enter_bug.cgi?product=xorg

Select "Component" : "Driver/Radeon"

And in a second bug : "Driver/radonhd"

Describe the bug and the option, you had to choose. You can also link to this page.

If you have any questions, fell free to ask.

Thanks for making Ubuntu (and linux in general) better!