filtered drop down - validation

I'm trying to implement a filtered drop down for a BO "Car", e.g. "CarModel" filtered by the value selected on "CarBrand":

The dropdown-values of CarModel are populated correctly when I change my CarBrand, but the original choosen CarModel is not cleared.

Example:

1. Select "VW" as CarBrand and choose the "Golf" as CarModel -- save the Car-object.
1. Re-open the newly created Car-object and change te CarBrand to "Mercedes":
  the CarModel dropdown is re-populated, but the previous selected/persisted CarModel option "Golf" is not cleared. I can save the form without picking a new (valid) CarModel.
  (so I'm able to save now a car as "Mercedes" "Golf"...)

What rules do you have to populate the drop downs?

I didn't define any rule. I've only created a custom query to filter the values on the CarModel dropdown by the selected brand-value of the car:

So, the presentation of the Car.model-attribute has this custom filter:

FIND CarModel WHERE CarModel IN Car.brand.models

Which Aware IM build are you using?

v. 4.9 (build 1372)

We are releasing version 4.95 early next week - check if the problem is present in the new version

..and you offered to provide an early look to tested out. I don't NEED that, but will be happy to apply it and report the results if that helps you.