Manage display arrangement errors in OS X
When you connect an external display to your Mac, the system will usually by default resort to its native resolution and arrange it to the right of your main display. You can modify these settings in the Displays system preferences, which should preserve separate settings for each display you use with the system; however, after updating or upgrading OS X the system may not keep these changes and persistently revert to defaults every time your display is attached or when the system restarts.
If you use the default arrangement then this issue may not be much of a problem, but … Read more