total climbing & reset elevation

Hello, whenever I upload a route via garmin to the route manager, and press 'reset elevation' it goes totally ballistic and calculates HUGE climbing values.  I could upload a route and save it, and then upload the same route and hit 'reset elevation' to show as an example if that would help. Is this feature not working, or am I using it incorrectly? 

I've used sports tracks and mapmyride to get totals for elevation ascent and they are all different, but the 'reset elevation' total is usually much much greater than any of the others.

Whats the most reliable way to determine total climbing?