Was probably not 'one button' that was pressed. I suspected DND at first, but I enabled and disabled that one already.
Button 1 - 7:
Call1
Call2
DS22 ->DS
DS ->DS
NONE
DS25 ->DS
SPD500->SPD

Button 6 above flashes rapidly on this extention on incoming calls. On EXT2 it is button 7. Both are DS25 under 107.