staffgroup-staff-spacing may be applied multiple times per StaffGroup

[Thomas Morley]

Hi,

for nested container-contexts StaffGrouper.staffgroup-staff-spacing is
applied not only to the last Staff (as opposed to the NR).
See code below, png attached.

\version "2.19.82"

mus = \new Voice { c''1 }

\score {
<<
\new StaffGroup
<<
\mus
\new GrandStaff << \mus \mus >>
\mus
\new GrandStaff << \mus \mus >>
\mus
\mus
\layout {

%% Play with the padding-values
\override StaffGroup.StaffGrouper.staffgroup-staff-spacing =
#'((basic-distance . 0)
(minimum-distance . 0)
(padding . 10)
(stretchability . 0))
\override GrandStaff.StaffGrouper.staffgroup-staff-spacing =
#'((basic-distance . 0)
(minimum-distance . 0)
(padding . 0)
(stretchability . 0))

%% Don't get disturbed by other settings
\override Staff.VerticalAxisGroup.default-staff-staff-spacing =
#'((basic-distance . 0)
(minimum-distance . 0)
(padding . 0)
(stretchability . 0))
\override StaffGroup.StaffGrouper.staff-staff-spacing =
#'((basic-distance . 0)
(minimum-distance . 0)
(padding . 0)
(stretchability . 0))
}
}

http://lilypond.org/doc/v2.19/Documentation/notation/flexible-vertical-spacing-within-systems
states:
"Properties of the StaffGrouper grob
[...]
staffgroup-staff-spacing
The distance between the last staff of the current staff-group and the
staff just below it in the same system,
[...]."

Actually, the last Staff of a StaffGroup (or equivalent) _and_ every
Staff right before another container-context is spaced by
staffgroup-staff-spacing.

I'm undecided whether I'd call this behaviour a bug or a feature.
Opinions?

In any case the doc is currently wrong, at least incomplete.

Cheers,
Harm