Rain tracked?

Hi there,

I am using Digi-effects RainFall, and I ran into a problem.
I have a moving shot of an outdoor steps. I traced a SHAPE layer on the handrail and tracked it so it covers the railing. (this will be where the rain bounces off of)Then, I added a SOLID LAYER and added the rain effect. All works great.The rain bounces off the railings. BUT!..as soon as I Parent the RAIN layer to the Tracking data, the rain effect gets all screwed up. To understand what i mean, do these steps..
1
make a solid with rain on it.(Generate alot af rain)
2. Add a small shape layer (make a weird shape)
3. Make the rain bounce off the shape layer. (Via splash settings)
ALL should work fine up to this point....
4.make the Rain layer pan from left to right. ( key Position)
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Hopefully, you will see that the splash line is created at frame 1 and then it stays the same shape while it pans.It's not updating the shape as it rain travels.

QUESTION:
So, how do I make the RAIN LAYER move while it follows the SHAPE ?

Does this make sense?
Thanks,
Lou