Beam/Stem misattached (v2.7.28, WinXP)

[Thies Albrecht]

Hi everybody!

Using Lily v2.7.28 on WinXP compiling the example below I get the 
following error:

The stem of the last eigth note in bar #1, staff #3 is a bit to long.

This behaviour varies when altering the input code. For example:

1. Removing every Staff.instrument -> error seems to be fixed
2. Completing the last bar in every staff -> all four stems are
   misattached

It gets even more strange in my full score: Depending on whether I put a 
fermata mark in staff #1 the beams/stems are misattached.

Any hints on solving this problem are welcome. Also any link to the 
bug/user-list, where I couldn't find a solution yet.

Kind regards,
Thies Albrecht

Example:
--------

ottavaOn      = #(set-octavation 1)

ottavaOff     = #(set-octavation 0)

%----------

global = \relative c'' {
      \key c \major   \time 4/4   s1*1   s2   \bar "|."
}

InstrI = \relative c'' {
      c,1 ~
      c2 ^\fermata
}

InstrII = \relative c'' {
      c,2   <f a>
      <e g e' g c>2 ^\fermata
}

InstrIII = \relative c'' {
      r2   \ottavaOn   c8   f   a   c
      e2 ^\fermata   \ottavaOff
}

%----------

\paper {
      raggedright = ##f
}

%----------

\score {
      \context StaffGroup = "InstrI-III" {
            \override Score.BarNumber #'padding = #'2.0
            <<
                  \context Staff = "I" {
                        \set Staff.instrument = \markup {"Instr. I"}
                        \override Staff.VerticalAxisGroup #'Y-extent = 
#'(-5 . 5)
                        <<
                              \global
                              \InstrI
                        >>
                  }
                  \context Staff = "II" {
                        \set Staff.instrument = \markup {"Instr. II"}
                        \override Staff.VerticalAxisGroup #'Y-extent = 
#'(-5 . 5)
                        <<
                              \global
                              \InstrII
                        >>
                  }
                  \context Staff = "III" {
                        \set Staff.instrument = \markup {"Instr. III"}
                        \override Staff.VerticalAxisGroup #'Y-extent = 
#'(-5 . 5)
                        <<
                              \global
                              \InstrIII
                        >>
                  }
            >>
      }
}

%----------