Two distinct pitches of same letter need explicit accidentals

[Jon Arnold]

> I'm not top posting.

Hi-

Pretty sure this is a bug or could be handled better. Hopefully it hasn't been 
reported already

Snippet:

%b-flat disappears
{\key f \major
<< {c'' b'} \\ {a' bes'} >>
}

This produces (ignoring stem direction): <c a> b (as in b natural)
Image: http://imgur.com/1FwQyzm

In fact, <c a> <b bes> has a similar effect. The b-flat is effectively missing.

Hope this is helpful. Please CC me in replies.