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

(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.