Passing variable for ng-true-value to directive in AngularJS fails

I do have a directive input-checkbox as a template for <input type="checkbox" .... I am trying to pass values for ng-true-value to this directive and here I am stuck:

I am using the directive like this:

 <input-checkbox ... mv-true-value="false" mv-false-value="true"  mv-disabled="true"></input-checkbox>

and the directive template looks like this:

        <input type="checkbox" ...
           ng-disabled="mvDisabled"
           ng-true-value="mvTrueValue"
           ng-false-value="mvFalseValue">

The value für ng-disabled is correctly compiled as "true" but ng-true-value and ng-false-value are not correctly set.

To narrow down what might be wrong i tried different stuff: This works as aspected:

            <input type="checkbox" ...
           ng-disabled="mvDisabled"
           ng-true-value="false"
           ng-false-value="true">

Also this works as aspected:

            <input type="checkbox" ...
           ng-disabled="mvFalseValue"
           ng-true-value="false"
           ng-false-value="true">

WebStorm tells me ng-true-value is not allowed here but as described above it still works if I set fixed values in the template file. I am working with AngularJS 1.7.2

Any ideas?

EDIT: I forgot this information. The scope in my .js for the directive looks like this:

 scope: {
 ...
  mvDisabled: "=",
  mvTrueValue: "=",
  mvFalseValue: "=",
 ...
}