Dual headed trains will reverse directions without slowing down if manually told to go to a stop in the opposite direction of they are currently traveling.
Thanks for the report however this is not an interesting corner case we are willing to handle. If a train would be modded it could have a significant weight and if it would have to first keep path in the old direction with all the reservations and only after stopping fully would be allowed to go the other way around by the time it stopped it could already cross one way signals and not be able to move the opposite direction. It is a simplification made to avoid ugly corner cases that are not fun either for us and not fun for players.
Other than that i am considering this to be a duplicate of 50266 as it has the same root cause: train is forced to go the other way around and it stops.