When a customer changes a setting in the video tab, the selected video mode will also change name.
Standard
will change to:
Standard (User)
A user can only get rid of this by resetting the picture settings.
When a customer has wrong picture settings, but you can not find the cause, check if it says (user) behind the video mode.
If it does, then you know the customer has changed this setting and this might be the cause of the problems.