Soft particles not appearing when they collide with distortion effect

My scene has a distortion effect. It looks like this:

It works via a particle system which outputs a single particle that increases in size over lifetime. Its shader just renders a normal map to texture. It works fine when "Soft Particles" is turned off in my quality settings.

Unfortunately, when "Soft Particles" is turned on in the quality settings, any particle onscreen doesn't show up under the distortion effect.

This is a big problem for me, since there are a lot of dust clouds in my game, and when I create a distortion effect, they don't appear under the distort. In fact, you can see where the edges of the distortion effect meet the particles. It ends up looking like this:

As you can see, the outline of the distortion effect is clearly visible, and it looks terrible.

My guess is when the distortion effect takes a snapshot of the screen, to render it to texture, it isn't capturing the soft particles.

Any suggestions would be very helpful.

Thanks.