Wrongly read property with MetronomeMark

[Thomas Morley]

Hi,

the following code

{
  \tempo 4 = 60
  \override TupletBracket.after-line-breaking =
    #(lambda (grob)
    (format #t "\nstyle is: '~a" (ly:grob-property grob 'style)))
  \override TupletBracket.style = #'dashed-line
  \tuplet 3/2 { 2 2 2 }
}

prints in terminal:

style is: 'line

As soon as \tempo is commented 'dashed-line is written.
This happens at least since 2.21.6
2.20.0 is ok

Cheers,
  Harm