cross-staff stems for only two of three staves

[Malte Meyn]

Hi list,

I would like to set cross staff stems in a three-staff piano score. With 
stems from the middle to lower or upper staff everything works fine but 
not the other way (from outer to middle staff). Does anyone have an idea 
how to fix that or work around?

\version "2.19.30"

\new PianoStaff \with {
  \consists #Span_stem_engraver
  \autoBeamOff
} <<
  \new Staff {
    e'8 f'
    \crossStaff e'' f'' % not ok
  }
  \new Staff {
    d'8 \crossStaff e' % ok
    d'' \crossStaff e'' % ok
  }
  \new Staff {
    \crossStaff c'8 d' % not ok
    c'' d''
  }
>>