Interesting accidental placement with Score.modern style

[Kevin Pye]

I'm engraving a score using Score.modern accidental style. I have a repeated 
chord with an F♯ and an F♮ above it. If you set it with just "<fis f'> q" then 
lilypond adds a natural symbol to the F in the second chord, presumably to 
cancel the sharp in the first chord. If I explicitly add a natural sign to the 
first chord, I still get the sign on the second chord. The original material 
has accidentals on both notes in the first chord, and none on the second, which 
seems more natural.

If further chords are added, they all have the natural sign on the top F.

Any ideas on how to set this more naturally?

Example:

\version "2.25.9" 

\new Staff \with { \accidentalStyle Score.modern } { 
    \new Voice { <fis' f''>4 q } 
} 

\new Staff \with { \accidentalStyle Score.modern } { 
    \new Voice { <fis' f''!>4 q } 
}