PC Hhl Red Signal Went Black When I Stopped And Vanished From Hud

Playing Turnback Freight, after departing Lubeck Hgbf I encountered a red signal near the exit from the yard. I stopped at the signal and it went black and vanished from the next signal HUD. Its not game braking "Contact Signaller" gets a proceed at restricted speed. Is this a deliberate simulation of a signal failure or a bug?

Paul

 

Note, as soon as I started to move it reappeared on the HUD with a yellow aspect and showed a single green light on the signal itself.