Cross-staff beam problems (collisions & ugly slope)

[Marcus Macauley]

\version "2.18.2"
\paper {indent = 0\mm ragged-right = ##t}
up = {\change Staff = "upper" \voiceTwo}
down = {\change Staff = "lower" \voiceOne}
  \new PianoStaff <<
    \new Staff = "upper" 
    \relative c' { \time 1/4 \omit Score.TimeSignature
%%%%%%% Beam collides with notehead; ugly beam slope:
      \up d16 \down f d f \break
%%%%%%%% Beam collides with accidental:
      \up d \down f! d f \break
%%%%%%%% First & last beam groups have correct minimum stem length and
horizontal slope;
%%%%%%%% Other beam groups should maintain same minimum stem length by
forcing staves apart;
%%%%%%%% Other beam groups (arguably including middle group) should have
horizontal slope:
      \up d f d f
      \up d \down f d f
      \up d f \down d f
      \up d f d \down f
      \down d f d f
    }
    \new Staff = "lower"
    { \clef bass s4*7} >>

The example above is my attempt at a "tiny" illustration of three
simultaneous problems with a cross-staff beam: collisions (of beam with
notes or accidentals); ugly slopes; and ugly horizontal spacing (stem
spacing overcorrection).

I checked the Lilypond Google Project Bug Tracker before making this, and
the most similar issues I could find were 1324 and 1702, but I don't believe
this is fully redundant.

Since I'm neither a programmer nor closely involved with this project, I
thought the best thing to do would be to post this example and hope that one
of you will know what best to do with it.

Marcus Macauley

P.S. I would have liked to begin this message with the introduction,
followed by the code, but when I tried that, the web form insisted that I
was "top-posting".