No event bubbling through animated bitmaps

bubbling events through a hierarchy of nested DiplayObjects works in many cases but
unfortunately it does seem to work not in all cases:

Given some nested Objects like so:

box = new Sprite();
box.addChildAt(containerA,0);
box.addChildAt(containerB,1);
box.addChildAt(containerC,2);

whereas containerA has some “clickable” Objects inside.

If containerB/C contain bitmaps, for instance, the event bubbling works.
But if containerB/C contain a bitmap with a bitmapData which is manipulated via setPixel
or other pixel changing methods, there is NO event bubbling any more.

My first guess was that has something to do with lock() or unlock() the bitmapData, But it hasn’t.

Does someone know why there is no event bubbling in such a case :q:

Keith