Render order with transparency


I got a very basic scene with three transparent spheres in a row, but I cannot reach a correct rendering order. It seems to me that the render follows the order in which the spheres have been added to the scene (ie, last added object is always in front of the others).
This is a screenshot that shows the issue:

The green sphere should be in the middle of the others.

I’ve also tried with setUseDepthPeeling(true) but I can see no effects.

Is there something else I should be aware of ?

Thank you

This is referenced in that issue