I'm having this issue on my HP Envy 17-2070nr with a Radeon HD 6850M. I'm using Ubuntu 14.04.
Here's info. for anyone who can help:
- Extended desktop causes internal monitor to show 1/2 of its own monitor and 1/2 of the external monitor's screen with a vertical separation (left and right halves).
- The other 2 halves are shown on the external monitor.
- Each screen (internal and external) works fine independently.
- Mirrored mode (both showing the same desktop) works fine.
- Extended desktop also causes non-stop display flickering to each monitor.
- Taking a screenshot of the extended desktop shows a normal extended desktop with each monitor functioning properly.