Adding value to scale only affects X, not Y? Why?

So I I'm using Sound Keys to drive the scale of another layer. However, it's only modifying the X scale, not X & Y.

What's wrong with this expression:

transform.scale+thisComp.layer("solid").effect("Sound Keys")("Output 1")

also tried these, but got an syntax error:
s = transform.scale+thisComp.layer("solid").effect("Sound Keys")("Output 1");
[s[0],s[1]]

and
s = transform.scale+thisComp.layer("solid").effect("Sound Keys")("Output 1");
[s,s]