I have two monitors, the primary monitor plugged on HDMI port has a 1920x1080 resolution, and the secondary monitor plugged on DVI port is a 1600x900 resolution monitor, but the second monitor configuration shows the 1280x720 as maximum resolution available. In others OS the second monitor gets the 1600x900 resolution as default. I think it's a really good information to say, the computer has a Nvidia GeForce 750, and using the Ubuntu nvidia-* drivers instead of opensource drivers.
Thanks in advance. :)