Let's say a person buys a train ticket from A to B, let say from Brussels Airport to Brussels Central Station. The ticket states that in order to be valid, you need to pay a second fee, a special fee because this is the airport transportation route. The person refuses and goes onto the train anyway. What crime did the person commit? A ticket violation or Fare dodging?
You get a similar situation when it comes to parking. If a person has a valid parking ticket but are parking when they are cleaning the street (i.e. during a no-parking period), the violation is not a parking ticket violation. It is a parking violation, just like any other parking without permission. The fact that the person has an ticket doesn't change anything.
Breach of contract against the ticket holder is very unlikely. Breach of contract against the ticket seller is possible. In the end, the most likely outcome of a person without a valid ticket is that they get treated exactly the same as a person without a ticket at all.