I consider this "bug" a feature:
If you have a round button with a large drop shadow, you need a large transparent square area around it to be part of the button graphic (not to cut the shadow).
So much that different round buttons, placed close to each other, actually have overlapping (rectangular) real estate, where the transparent area of can get on top of the opaque shape of the other. This is a real pain, as the wrong button will get executed when trying to press the underlying button!
Hence this "feature": only (partly) opaque areas are click-able, transparent areas "fall through". I use this all the time :-)
(But I agree it could have been more consistent between panel and simulator and better documented by Philips :-)