Composite behaviour for 3 tracks

Hi,

The behaviour of the Composite transistion seems a little bit strange to me: I'm not sure if it's a bug, but I fail to grasp the logic.

Let's say you have two clips : one green on track 3, one blue on track 2, and Composite transition between the two, with 75% opacity.
The result is as expected: you can see both, the blue one being more visible.
But if you add third clip, red one, on track 1 with a Composite transition at 100% opacity, you will see the red clip at 75%, the green one (bottom) at 25% but blue one will disappear.
I expected to see only the red (top) one.

So, is this a bug or did I miss something?