I've got a 2003 Sat Nav System in mine . I don't know if they are the same. But mine always calculates distances and times from the actual place the car is parked.
Are you pressing the Home key first(Start point) then going on to put in your Destination. As this will set up a 2 point destination route. You only need to put in Destinations.
The Home setting can be changed .
Press Menu -Marked Points -Delete Home then it will say are you sure so then Yes.
Do the same again Menu -Marked points but Delete Home will how say Register Home
Mine has 5 presets Home being one of them .I hope this helps