exchanged accidentals in MensuralVoice?

[Werner LEMBERG]

[lilypond 2.11.20]

Looking at section 7.7.12, `Mensural contexts', it seems to me that
the sharp and flat accidentals are intermixed.  The `fis' looks like
having a flat accidental, and the bes as if it had a sharp sign.

My knowledge of ancient music is too limited to decide whether this is
correct or not.  In case it is correct, it would probably deserve a
comment somewhere.


    Werner