So here are the issues. They can be seen on the swedish server game.
http://list.extended.simutrans.org/~vladki/debug-saves/t-signals.sveA: at loading the game - T-signal at Bockara is at Caution (East) - well it is an absolute block signal, how can it possibly show caution? It will remain at caution (east) until the train reverses and departs. I think it should turn to danger when the train stops, and show clear (west) for departure. (For arrival either danger, or caution east, makes sense).
B: at 3:04 another train arives to Tun. There is another train in Fageras scheduled for Tun as well, and it will depart immediately, when train in Tun stops. There is only the T-signal at Tun station (no home/choose signals). I think the train in rear should wait until the first train departs. Otherwise there is a potential for deadlock. Interestingly the T-signal at Fageras is at danger all the time when train is departing.
C: at 3:20 two trains approach Klovertrask almost simultaneously, they both slow down to 1 km/h, crawl for 2 tiles, and then speed-up again before finally stopping and loading. The T-signal does funny dances, being clear-east for most of the time, then shortly jumping to clear-west, back to clear-east, and finally to danger. Train departing westwards, departs with signal at danger.
D: about the same time as both trains depart from Klovertrask, th 3rd train arrives to Tun. It stays there waiting for clearance, but the T-singal show clear-north (3rd train is heading north). At about 3:44 train from Klovertrask arrives, and slows down to 10 km/h, signal then changes to clear-south, train accelerates, and the other departs, turning the signal to danger. Again train to the south departs at danger.
I have tried changing the dat file to aspects=2, but it did not help, just the signal disappeared competely at some aspects. What helped was to put home (choose) signals in front of the station. This reduced the chance that there would be simultaneous reservations from both directions up to the T-signal which seem to be the cause of case (C).
I have also tried the same layout with time interval with telegraph T-signals, and it worked much better, but the trains still slowed down to 10 km/h like in case D. Maybe I was just not lucky enough to spot the exact situation as C with time interval. I also suspected that direction (W-E), is the problem but it behaves the same after rotation.
Maybe Ves should comment on how the t-signal is supposed to work, and perhaps accept some changes from real world (which we are not sure how it really worked). Just to make these signals more intuitive and predictable.
I think the T-signal should really signal only departures, and not arrivals. That should be signaled by home signal (choose signal, plate signal).