If there is no signal at the end of a station when a train is in an absolute block, it will then travel at 1 km/h. This is easily done when putting signals at the end of stations and missing one.
If I open up the schedule then train will temporarily speed up to 30km/h before dropping back down to 1 km/h.
I've attached a savegame using pak192.comic-extended, using nightly build of simutrans-extended and with local built copy from commit on Github (https://github.com/jamespetts/simutrans-extended/pull/678/changes/bcd24ddeeebea250db2f928ad95865f391d6a496b).
Suggested behaviour: Switch to drive-by-sight.
This is also observable when at an end-of-signalling sign in certain circumstances where two convoys are close together.
BTW the URL and link text are the wrong way around.