Yes I got a solution
First of all, it seems that this is a GarageBand bug. I can confirm that it behaves that way also on my machine (BTW same procedure in Logic, works fine)
Here is an easy fix: Create a single Automation Control Point, that will stick.
(I will explain the Automation and all the rest of the new features and details in my new GarageBand X book, available very soon.)
Hope that helps
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