Stave properties: "Do not hide if system is empty" not working!

In the attached score, I want the organ pedal part to be hidden except where it contains notes, so I've selected "Hide empty staves" in Style | General | Score and deselected "Don't hide empty staves in first system". This is working fine. However, I do want the vocal parts to be displayed when empty, so in each stave of the voice parts, I've selected "Do not hide if system is empty" (should that be "if stave is empty"?). But if you look at page 3, where there is no Alto and Tenor, and page 4, where there is no Soprano or Alto, the empty staves are missing.

Is there something else I should have done, or is this a bug?

I'm using Musescore version 2.2.1 revision 51b8386.