Loopback 4: setting "strict mode" on models to false

It seems like when I turn off “strict mode” on a model (in decorator settings:{strict:false}) for the purpose of allowing custom model properties, I still get a ValidationError as the parent constructor is called. I have to remove this property key from the Partial data object before calling the parent constructor, and then I can add safely add the value after the parent constructor is called, like this:

constructor(data?: Partial<User>) {
  let user_role;
  if (data && data.user_role) {
    user_role = data.user_role;
    delete data.user_role;
  }
  super(data);
  if (user_role) {
    this.user_role = user_role;
  }
}

The error:

The `Users` instance is not valid. Details: `user_role` is not defined in the model (value: undefined).

Is there a clean solution I'm not seeing?