GPU particles are culled in front of the background

Hi,
I’ve got a particle system (a fountain) made by GPU particles. In my scene there is a PostProcess effect that let only see a circle (basically, a radial gradient world defined, which exterior is set to black to “hide” the rest of the scene).
With this setup my fountain is like chopped when the droplets are in front of the hidden parts of the scene. Any idea which parameter I have to change ? In the particle emitter, material, actor parameters, Postprocess material ? I think I’ve tested everything but I probably missed something… Thanks !

Here are some precisions :

(MF_* functions come from Chameleon plug-in, I’ve removed them and the effect is the same in this setup)

Looks like the problem comes from the particle material set to Translucent. Opaque and masked are not culled (but don’t render well for such an effect). Any advice ?