Compound audio clip, trying to set two 'different' keyframes?

A puzzle. I've turned my audio clips/tracks into a compound clip. I wanted to do a very slow crescendo over two minutes, using keyframes. I set the two keyframes, beginning and end of clip, but when I move one, the other also moves, as if they are locked. So I can't do this imagined crescendo.

I seem to remember doing this easily in the past. Is there some kind of convention with the compound clips such that I can't do keyframe adjustments?