Since i have Maps 3.0 installed, the sports tracker and also other software does not get enough computing power in the background. Sports Tracker does sometimes not store one GPS point for several kilometers !!!
Once switched to foreground, or when maps 3.0 is switched off, then everything works great.
I assume this has to be changed in OVI maps.... but unfortunately the support of NOKIA did point out that Sportstracker is beta and i should ask for help here. And i have no idea if i have the chance to modify priority-settings of running applications....