I just checked and this is working OK for me, I may know what is going on though.
When you initially assigned zones to your vehicles, how did you go about this?
Method #1
1. Click vehicles in Tree view.
2. Select vehicle in the List view, right click > Properties, add a zone on vehicle tab.
3. Then create a routing folder and add vehicles.
Method #2
1. Create routing folder and add vehicles.
2. In the routing folder, right click vehicle name > Properties, add a zone on vehicle tab.
The difference above is that in method #1, you're creating a template route which will be added to all new routing folders you create. In method #2, you're only adding a zone to a vehicle in one specific routing folder.
In your case the problem might be that you edited the properties of the template vehicle to add more zones. This would then be reflected in any new routing folders you created, but not for existing routing folders. You'd need to actually edit the properties of vehicles within the routing folder you've already created routes for. When I do this, I get similar results to what you're describing and it looks like nothing is happening.
Hope this makes sense, if it's not the issue, we can look at what else may be going on.