Flex :: Flash - Can No Longer Assign Class Property Values

Given a dynamic or non-dynamic class like the following:
package {
public class MyClass {
public var myProperty:String;
public var myBooleanProperty:Boolean;
public function MyClass() {}
}}

Flex 3 allows you to assign a value to myProperty like this:
myClassInstance["myProperty"] = "myValue";
myClassInstance["myBooleanProperty"] = true;

I regularly parse XML to get property names and their values then update correlated classes using this technique; however, Flex 4 no longer allows assigning the boolean property. I don't have a work-around.

If you trace the results:
trace(myClassInstance.myProperty) // Returns "myValue"
trace(myClassInstance.myBooleanProperty) // Returns null