I want to share a problem I had with my SP4, that was driving me crazy:
Each time I ran some programs like Apple’s iTunes or VLC Media Player, the screen brightness went to the highest possible value (even blinding my eyes).
After some Googling I found out that it was caused by a setting in my BitDefender antivirus: the “Active Profiles” feature.
These Active profiles changes the Surface’s power mode to “High performance” and maxes screen brightness to the max while playing videos or games.
In order to disable it, you have to go to Tools –> Profiles –> Configure and then in Movie Profile –> uncheck “Adjust Power Plans for Movies”.
Hope that helps someone!
Regards from Spain,