I'm sorry. I have to reopen this thread.
: Created a track by add / measure route = _First.gpx = w/out time tag.
: Than cutted this track twice = _First_01.gpx, _First_02.gpx, _First_02_01.gpx, _First_02_02.gpx = each w/out time tag.
: Created a new track = 3.gpx = w/out time tag.
: Than i merged _First_01.gpx and 3.gpx.
: The merged track _Final_with_time.gpx contains time tags with worthless values

So i guess there is a code snippet left in function for merging tracks.
@menion: can you please change this also?
Many thanks,
Christian