Hello. I haven't found if it is a known bug.
If the first note of a measure has an accidental, in one-staff music it avoids
the preceding barline correctly.
But in piano systems this avoidance does not work, LP seems to believe that the music is still in a single staff because low-pitched notes (and
high- I suppose) place more at the left, as if there were not any barline between staves.
Note that first e,! does not collide, but first e,! in third measure does. If
it were an e' I wouldn't.
%begin
upper = \relative c' {\key f \minor \time 12/8
r4. r8 r r r r r r r r
e8 e e e e e e e e e e e
e, e'! e! e! e! e! e! e! e! e! e! e!
}
lower = { R1. R1. R1. }
\new PianoStaff << \new Staff \upper \new Staff \lower >>
%end
see http://www.paconet.org/lilypond-translation-es/alter-colission.pdf