Stem across piano staffs

[Joseph Haig]

Some time ago I found a way of getting a stem to extend across two
piano staffs, shown in the code below.  This works with 2.10 but with
2.11, it seems that the long stem length causes extra space to be
added between the staffs, so they never join up.  Does anyone have a
fix for this, or could recommend a different way of getting this
effect?  The two attachments show show this sample in 2.10.33-1 and
2.11.55-2.

Regards,

Joe

stemExtend = \once \override Stem #'length = #22
noFlag = \once \override Stem #'flag-style = #'no-flag

\new PianoStaff <<
  \new Staff \relative c' {
    d8
  }
  \new Staff \relative c {
    \clef "bass"
    \stemUp
    \stemExtend \noFlag <f a>
  }
>>

test-2.10.pdf
Description: Adobe PDF document

test-2.11.pdf
Description: Adobe PDF document