I've got an R530 running Ubuntu 10.10 (although this has also happened in Linux Mint and Arch Linux). I'm using a 19" external LCD. When the computer starts up, the resolution on laptop and external LCD are correct (I previously set them to both be at their native resolutions). About 10 or 20 seconds later, the display reverts to mirrored (both screens show the same picture) and the resolution goes to 1024x768 on both.
I'm using the following shell script to fix it:
xrandr --output LVDS1 --mode 1366x768 --output HDMI1 --mode 1280x1024 --left-of LVDS1
After I run this the screens stay correct for the rest of the session, but after a restart I get the same problem. Any ideas?