Good to know. And it does make sense as described in the comments. This is for my future reference and for others who may experience it.
In a nutshell, if you have a getter/setter pair and make them [Bindable], the setter will not execute again if the new incoming value is the same as the current value. That speeds up performance but if you always need to check that value, it might be a bit confusing why it’s not executing.
As soon as you make the getter/setter bindable, Flex stops running the setter whenever the value you’re sending in already matches the value that the corresponding getter will return.
The solution (or at least one solution) is not to rely upon the default propertyChange event which is dispatched for bindable values, and instead create/dispatch a custom event