Many thanks for your email in regards to the 'start' button popping up when you enter a profile.
It is popping up as it is prompting you to start 'recording your activity', this is good practice as you may want to do a backtrack and ask the GPS to take you back the way you have come during your activity.
Therefore by just pressing the 'start' button will reset both your trip computer and start that track (which is a record of your trip).
Once you have pressed the 'start' button it will not pop up again.
Even if you are just wanting to look at other things within your unit just press the start button and it will stop it popping up for you again.
I hope this helps.