http://support.tixati.com/bandwidth%20presets
Help pages aren't up to date, you can set a preset as Downloading Default and another one as Seeding Default. Those two are switched automatically. When all transfers are seeding the Seeding Default is active, when a downloading transfer is added Tixati switches to Downloading Default. The problem is those changes are based only on transfers status. If a torrent is incomplete and stalled by weeks or extremely slow, the automatic switching doesn't work. To be more specific, the Downloading Default is always on, although there isn't any real downloading or there is but at very low rate.