As I understand elevation data is retrieved from TCX files while dismissed from GPX. As I understand this was done because GPX format is used by wide variety gadgets and its hard to handle elevation.
I have Xperia Active which has integrated barometer and I wish that elevation data would be taken directly from GPX. Maybe it would be possible to have an option on GPX upload: to use GPX elevation data?
At the moment I found workaround: convert GPX to TCX, but it is not straight forward as to simply upload GPX.