System don't remember primary monitor (in a dual monitor setup) after finishing session

[Antonio Camargo]

I've just added an extra monitor (VGA) that I want to be on the right of my main monitor (DVI).
Ubuntu automatically recognized the new VGA monitor as the primary, so the Unity's launcher stayed at it, even though I wanted the launcher to stay at the main monitor (the one that is on the left). As I could'nt choose the primary monitor in Ubuntu's settings, I had to use the NVIDIA X Server Settings to do it (screenshot).
After choosing the DVI monitor to be the primary one, the launcher went to the right place. But, after finishing the session and entering it again, the monitor on the right turned back to be the primary one and the lancher went to the wrong monitor again.

The only way I found to fix this was editing "/.config/monitors.xml", changing <primary>. Now, it is like this:

<monitors version="1">
  <configuration>
      <clone>no</clone>
      <output name="DVI-I-0">
      </output>
      <output name="VGA-0">
          <vendor>GSM</vendor>
          <product>0x43cc</product>
          <serial>0x01010101</serial>
          <width>1280</width>
          <height>1024</height>
          <rate>60</rate>
          <x>1680</x>
          <y>118</y>
          <rotation>normal</rotation>
          <reflect_x>no</reflect_x>
          <reflect_y>no</reflect_y>
          <primary>no</primary>
      </output>
      <output name="DVI-I-1">
          <vendor>SAM</vendor>
          <product>0x03e5</product>
          <serial>0x54573232</serial>
          <width>1680</width>
          <height>1050</height>
          <rate>60</rate>
          <x>0</x>
          <y>0</y>
          <rotation>normal</rotation>
          <reflect_x>no</reflect_x>
          <reflect_y>no</reflect_y>
          <primary>yes</primary>
      </output>
      <output name="HDMI-0">
      </output>
  </configuration>
</monitors>

[Daniel van Vugt (vanvugt)]

The primary setting is specified in xrandr, and that is populated by the graphics driver. So it's an nvidia bug.