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.
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.