If you place two overlapping shapes in a stack pane and create a timeline which fades the stack pane's opacity slowly from 1 to 0, what happens?

Let us say the shapes are a square with a triangle on top. Intuitively, I would expect the fade to mean that the rendered pixels of the stack pane become more and more transparent until the stack pane is gone. But with JavaFX this is not so.

What actually happens is that each of the children inside the stack pane become more and more transparent, and as the front triangle becomes transparent, you can see through it and see the square behind it it.

For a human user this is quite surprising and odd looking. Imagine you where looking at the picture of Mona Lisa, and while the whole picture was fading you could suddenly look through Mona Lisa and see the landscape behind her…

In our UI framework this property of JavaFX means that some of our more complex controls look odd if we start fading the Pane in which they are shown. Instead of fading them as a whole, each shape used to render them become transparent, and the user can now see how they are constructed.

I have seen this with JavaFX on Mac, and it looks very unnatural because none of OS X's built in visual effects does this.