An undiagnosable screen fault (flickering/glitching)
If possible, try using a second display (through Mini-DisplayPort or Thunderbolt). 

The objective is to find if the issue is the LCD panel (Screen) or the GPU (Video Chip/"Card"). 

If the issue persists on a secondary/external display, the issue is the GPU. If the issue is limited to the built in display, you've narrowed down the source of the issue to your LCD. 

Have you noticed any other patterns, such as use of Safari or other apps? Some apps, upon opening, switch from basic "integrated" graphics, to the more powerful "discrete" graphics chip, and its possible that this change is causing the distortion.

EDIT: I should also note that service providers' diagnostics are unable to detect connection issues with the LCD panel (unless completely disconnected), so any tests they run will be inconclusive if its the LCD. LCD issues simply require visual inspection, and your photo should be sufficient proof. Source: Apple Employee/tech for 8+ years