0) I turned on the tracker around 15:00
1) the tracker stopped recording on it its own at 16:13 (the last recorded point)
2) I noticed this 20 minutes later and turned the tracker on and off
3) it recorded fine for the next 3 hours
4) again it stopped recording on its own at 19:15
5) the tracker stated that it was "on" when I checked it at 8 pm
6) interestingly, it stayed on even when I closed the application with the back button
7) the icon disappeared when I entered the application again and turned the tracker on and off.
There was very little going on with the phone except of the tracking. I was out of range of data connection, the AlpineQuest was the only application I really used except of
- listening to audio from 15:15 until 17:00,
- sending one text message around 16:30 (this is when I noticed the tracker problem mentioned in 3) and
- making three phone calls from 18:50 until 19:00.
For a moment I was sure that tracking was interrupted by the messaging and phone apps but from the above data unfortunately it is not that simple

I can upload the track, if it is of any help.