bug report: staff change doesn't work without a key signature.

[Peter Kölcze]

(I already sent this bug report two weeks ago, but I only sent the .ly 
file and I didn't get an answer.)

\version "2.26.0"
rh = \relative c' {
% \change Staff doesn't work without a key signature.
    \change Staff = "lh"
    c
}
lh = \relative c {
    \clef bass
    c
}
\new PianoStaff
<<
    \new Staff = "rh" \rh
    \new Staff = "lh" \lh
>>

The problem was already there in 2017: 
https://archiv.lilypondforum.de/index.php/topic,2501.0.html
The manual 10.1.2 Known issues and warnings says nothing about it.