GUIEffect: Issue with transitive @UI inheritance

We have observed some strange behavior for the GUIEffect checker when dealing with long (>2 classes deep) inheritance hierarchies.

Consider the following example code:

class MyTestCase {

    @PolyUIType
    static class PolyUIBaseClass {
        @PolyUIEffect
        public void foo() {};
    }

    static class TransitiveUISubclass extends @UI PolyUIBaseClass { }

    static class UISubclass extends TransitiveUISubclass {
        @UIEffect
        public void bar() {}
        @Override
        public void foo() {
            bar();
        }
    }

}

Unless I am mistaken, I would expect the guieffect checker on this code to compile without error (which is what happens if UISubclass is made to extend @UI PolyUIBaseClass directly, except for a effects.redundant.uitype warning), or else to give an override error, where it complains that foo should be @UIEffect, as it overrides @UIEffect TransitiveUISubclass.foo().

However, instead, this code fails with error: (call.invalid.ui) on the callsite for bar(); inside foo, showing that it considers the declaration of UISubclass.foo to be both valid and @SafeEffect.

Is this expected behavior or an error in the checker?

cc: @msridhar @csgordon

p.s. This is not a high urgency issue for us right now, but it seems very unintuitive and did mean that in the past we weren't checking some things that we thought we were.