This happens occasionally with GPS.
Personally, I have not seen this much off with the GB-580P, but with other GPSes.
There are always "jumps" when entering / leaving tunnels for instance.
It could be improved by using the speed sensor, but I have not heard about any device using this data like this. (Some high-end running uses accelerometer though.)
There is an opportunity here for Globalsat...
Some GPS importers can filter the data based on for instance speed bumps. This of course dependent of how the filters are set, so not recording a flight are completely dropped.
You can export the track, edit it and reimport it.
Personally, I import into SportTracks that allows editing of tracks.