Transmission

That was it, the drive was mounted readonly.
Topic can close now.

Just can't figure out how Tm was able to write to it most of the time....

I never unmount it.
I have tried to automount it at startup, and I think I finally succeeded in this. It is an NTFS drive and in the settings I also discovered it was mounted default readonly. So this might very well be the cause.

My TM 2.50 (13228) on Ubuntu has troubles accessing the correct directories.
I have made 2 directories on my 2nd datahd. One for the temporary files and one for the complete torrents. This stashdrive is called "Toshdata".
This drive is not mounted at startup, I have to do that manually and do so ...