I have confirmed the issue on Ubuntu Gnome 14.04 but only when the monitor on the left is not the primary monitor. i.e. I can set my external monitor to be on the left of my laptop's built in screen, but only if I set it as the primary display. This might be important because, for me at least, it was not a "timing problem" but a configuration problem.
In case it's useful:
I have confirmed the issue on Ubuntu Gnome 14.04 but only when the monitor on the left is not the primary monitor. i.e. I can set my external monitor to be on the left of my laptop's built in screen, but only if I set it as the primary display. This might be important because, for me at least, it was not a "timing problem" but a configuration problem.
Working monitors.xml attached.