Never heard of this. For me it suffices that such a practice
might be confusing to beginners. There might be other reasons
why it might be desirable to have the B stem up or down. In
any case, neither way is correct or incorrect, so why complicate
matters?
--
For what it's worth, when I took music theory, we were advised (and this
is in consonance with numerous music copy tutorial books, I can quote
references for some if needed) to keep stems in one direction when
passing through the middle line of the staff.
Thus, for a scale starting on the bottom
\relative c'' { c b c } gives stem up, down and up. I would rather
have all stems down in such a case. Would it be possible tohave lily
do that ? The rule would be : if a `b' is between 2 `c' or `d' or `e'
in the same bar, the stem direction of the b should be the same as the
previous and next no
