tuplet numbers scattered all over the place when using manual staff-switching

[Hallstein Lunde]

Lilypond seems confused where to place tuplet-numbers when staff-switching is
involved.

\version "2.8.1"
csd = \change Staff = lower
csu = \change Staff = upper
\score {\relative c'
        \context PianoStaff <<
        \context Staff = "upper"   {\times 2/3 {f8 d c } \csd \times 2/3 {f, as 
a} \csu
\times 2/3 {c d f} g8. f16 |}
        \context Staff = "lower" { \clef bass <f,,! d'>4 s r2 |}
        >>
        
}