Adding part results in grand staff with two treble clefs

If I add a piano part with curScore.appendPart("piano"); it creates a grand staff as expected, but both staves have a treble clef, which is not expected.

As a workaround, I thought I'd select the treble clef and then call cmd("clef-bass") to replace it. Nope. Apparently I can't select the initial clef (I can deselect it if it's already selected, but if I try to select it I get "Cannot select element of type Clef"), but even if I could, cmd("clef-bass") can only insert a clef change, it can't replace the initial clef.

sigh

I'm not missing anything, am I?

Why does appendPart use the wrong clef in the first place?