In preview setting the layer opacity will display each shape as if it was transparent allowing underlying shapes to show through. This is incorrect. This is the bug. The whole layer should be transparent but not the individual shapes. Each shape is 100% opaque and should completely hide any shape below it. The layer as a whole has opacity but this should not effect the display of each shape.
Now we do a final render. The final render is correct. Each shape fill color is opaque over any underlying shapes but the whole layer is rendered at a lower opacity.
Technically this bug is not a deal breaker. You get the results you should but only in the final render. It can be confusing though if you don't know about this preview anomaly.
-vern
