Comment #3 on issue 2738 by [email protected]: Lilypond doesn't break lines http://code.google.com/p/lilypond/issues/detail?id=2738
It's the default behavior for LilyPond and most users count on it to find erroneous barrings. If you want to disable it, do:
\layout { \context { \Voice
\remove "Forbid_line_break_engraver"
}}
