I've got this issue with OSX El Capitan. My existing monitor show black border in resolution 1920 x 1080. The black border is shown only on left side of monitor. This never happen previously in Yosemite.
What I've tried but didn't work:
- set resolution in safe mode
- unplug and plug again my mini to VGA cable
- play with my monitor setting (reset setting)
Here is the screenshot:
Thank you for your help