Particles & object with transparent shader oddity

Hello,

I'm experiencing this odd effect when displaying a particle effect near an object with a transparent shader.

The images attached show when a "fire" effect is turned on "over top of" a plane with a transparent material.

Notice that the fire seems to go under the ground shadow plane? I'm using the stock transparent/diffuse shader for the ground shadow plane.

Any ideas how to stop this?

Thanks!

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Particles & object with transparent shader oddity