I did some research: "February 16th 2018 - qBittorrent v4.0.4 release - FEATURE: Add source field in Torrent creator. Closes #7965. (Chocobo1)"
More and more private trackers use the source tag to allow easy cross-seeding between private trackers. I would like to see the ability to set a source (or custom) tag in the qBittorrent torrent creator.
The above link also leads to a BiglyBT request with further comments.
Must be yet another control-freak wish of the private trackers. For Tixati will look like yet another comment but not-comment text field. Why couldn't they settle on a specific tag within the comment box?