Trigger Wheelslip?

In the scenario editor, if you apply the "trigger instruction" there's an option where you can intentionally make the player train have wheelslip. Now when you get the wheelslip when playing the scenario it seems as if it is impossible for the wheelslip to go away? I used the sander, nothing. I slowed down, nothing. I stopped the train and it was still giving me wheelslip somehow? This went on for a few minutes before I called it quits. Am I using the wheelslip option wrong? is it a bug? 
