tuplet, tremolo and cross staff

[Philippe Raynaud]

Hello,
I am typing a lied of Schubert (voice + piano).
In the Piano staff when I combine a tuplet of three 8 notes which crosses the
staff, everything is OK, but when the tuplet is in the \repeat "tremolo" shape,
the note above is correct (a 4 note dotted), but the note on the second staff is
a 2 note dotted (the double).
Anyway the midi output is correct (with \unfoldRepeats { }).

Example:
 \time 4/4  \key sib \major

UPPER: \clef treble

 \times 2/3 { \repeat "tremolo" 3 f8 }

LOWER: \clef bass

 \times 2/3 { \repeat "tremolo" 3 { \tupCrossB f8 } }

 where \tupCrossB means:
tupCrossB = {
 \stemUp
 \once \override Stem #'length = #22
 \once \override Stem #'cross-staff = ##t
 \once \override Stem #'flag-style = #'no-flag
}

I can send you an more complete extract on your demand .
Thanks in advance.
Phil.