Staff Grouping

[Dave Higgins]

> I'm not top-posting

\version "2.18.2"

\score { <<
        \new Staff { \relative c' { << { c1 } \new Staff { g' } >> \break
c,1 \break | << { c } \new Staff { g' } >> \break | c, } }
        \new Staff { \relative c' { << { b1 } \new Staff { f' } >> \break b,
\break | << { b } \new Staff { f' } >> \break | b, } }
>> }
\layout {}

I'm having trouble understanding why staff grouping isn't working.  If I
start with 2 parts that start with divisi staffs, that section is correct. 
When I go to a new divisi staff later on, the staffs are intermingled.  I'm
not sure if this is the expected behavior, but I've not been able to
overcome it (except through changing the parts).  Obviously, if one part is
compiled, the layout is correct.