Strange behavour of layout-set-staff-size

[Thomas Morley]

Hi,

while experimenting with test codes for issue
https://gitlab.com/lilypond/lilypond/-/issues/5977 I stumbled across:

\score {
  { \tempo 8 = 88 c'8^"toplevel Score" }
  \layout { #(layout-set-staff-size 40) }
}

\book {
  \paper { #(layout-set-staff-size 40) }
  { \tempo 8 = 88 c'8^"explicit book" }
}

Both in one file.
The text in the toplevel score is cramped. Output attached.
No idea what happens... Though, it's similar even for ancient 2.12.3
and all upstream versions.

Cheers,
  Harm