Comment 110 for bug 745112

OK, so kernel 3.2.0-030200rc1 seems to consistently behave like this:
 * boot up an x201 docked with dp connected to an external monitor
 * grub appears on both screens
 * plymouth appears on both screens
 * lightdm appears on both screens in low-res mirrored mode
 * unity session comes up with both screens blank
 * fn-f7 can get it back to mirrored mode
 * trying to switch to the external monitor does not work

What does work is, from the displays panel:
 * turn on both in mirrored mode
 * then turn off mirrored mode, but leave the external panel at a low resolution
 * set it to 1920x1440, and apply
 * then change to 2560x1600 and apply

so there is some path-dependency: full resolution will only work if you previously set it to a lower resolution.

i hope that helps.