My bike GPS, a Sigma one, the activities are always the same until you actively finish it. I mean, if I go for a ride, finish it and turn off the GPS, the next ride I will continue that activity. I have to actively finish the activity to start a new one. Nothing is sync until the activity is finished (to finish an activity I have to long press on button).
With this it is very difficult that you finish and activity unintentionaly and it is a nice solution for a multiple days activity but on the other hand you could end up with a very loooong, non intended, activity.
Maybe suunto should also ask for confirmation before finishing the activity.