The Global Positioning System (GPS) is influenced by many environmental factors. Each location is uniquely calculated and has its own accuracy associated.
A location determination at location X with an accuracy of 5 meters means that the real location is somehow within a 5 meter radius.
This is why the location can jump during the Live Mode, even when the Tracker is under a clear sky and not moving.
This behavior can seem odd especially when the device is indoors and the accuracy drops to 20-30m.
In Default Tracking Mode the location updates less often than in Live Tracking Mode, in which it updates every 4 seconds. This is why you might be able to notice the location jumping.
Further information about GPS can be found at the official GPS website by the US government: