/timername -e is executing the associated command of the timer by actually triggering the timer, changing the setting of the timer. It 'sets' the number of second left before the timer triggers to 0 which as a result decrease the number of repetition of the timer.
This behavior came as a surprise to me, the help file is also not mentioning this.
If this is a bug but can't be fixed because of backward comp, please consider adding /timer -eN with N = 0 (default) for the current behavior and N = 1 for just executing the command without changing the settings of the timer. Please also update the help file to be explicit about this.