AS3 event propagation thru alpha channel mask?

Ok, in AS2 I had a bitmap with an alpha-channel that made a transparent hole (mask) in front of external, loaded .swf files (aka rounded corners of an old tv). In AS2, events went thru the hole just fine and the swfs behind handled their events. After converting to AS3, and getting the swfs loaded again, the events do NOT reach the swfs playing behind the ‘mask’. Am I missing something or is this a major bug? Moving the external swfs to a higher level works, not the end of the world (I lose my rounded corners) but it proves the events don’t get to the layer that worked in AS2.