The negative elevations that I am experiencing seem more than just a GPS inaccuracy. I have had my Blackberry with GPS software running beside a Garmin Handheld GPS unit. When both units are set to read elevation from GPS signals only (not using barametric pressure to adjust), the Garmin unit would read an elevation of 1050m while the Blackberry would read -1050m. Other posts from other users have reported this similar negative elevation, where the whole number is reasonable but with a minus "-" symbol in front. This negative number is then recorded in the GPX tracks.