Hi,
a simple
\transpose c c'
(with changing stem-direction)
can break \crossStaff without printing a warning or error.
%%%%%%%%%%% example
\version "2.16.1"
\layout {
\context {
\PianoStaff
\consists #Span_stem_engraver
}
}
mI =
\new PianoStaff <<
\new Staff { d'8 }
\new Staff { \crossStaff { g'8 } }
>>
mII =
\new PianoStaff <<
\new Staff { \crossStaff { d'8 } }
\new Staff { g'8 }
>>
%% Good output
\transpose c c \mI
%% Bad output, no warning or error
\transpose c c' \mI
%% Good output, after manually fixing
\transpose c c' \mII
%%%%%%%%%%% end of example
-Harm