LilyPond needs a Staff context to be able to perform the \break
command, therefore if there isn't any such context alive for the
moment, LilyPond creates one.
Why not combine the two << ... >> sections into a single one and
just insert the \break command into one of the existing staves?
/Mat
In following fragment of code \break statement creates additional Staff context
"from
nowhere", and this Staff context lives until parent StaffGroup lives.
(GUB-2.7.39-1 under Linux)
/ak/
%%%
\version "2.7.39"
\score {
{
\context StaffGr
