I am not sure if this is the right place to report this bug, but I have tested it a few times and I can replicate each time.
If I create a class and add it to the interfaces and then I add a classifier to that class, the QoS does not take effect. And yes, I saved the changes and activated the changes.
If I create a class, then add a classifier then add it to the Interface, then the QoS does work.
Why is that?