This is probably similar https://forum.tixati.com/support/7451  but my situation is neither a pure bug report or feature request.

I had been partially seeding a torrent for a while, I decided to delete files locally but keep the transfer in Tixati (for Channel Share advertisements).

1. Go to transfer's Files
2. Select All, choose "Off"
3. Select All, "Delete"

Good: it removed all fully downloaded files, I can see the free space increased on disk
Bad: it did not remove pieces belonging to neighboring files. It still says 11 pieces complete.

I don't think there's any way to remove all pieces after deselecting deleting all files through Tixati. 10 x 16MiB pieces add up :)

Tixati 3.19