Hi Caio, Hi Malte,
Well there's something strange here: proportional duration seems to work in one feather direction only:
\version "2.19.35"
\relative c'' {
\set Score.proportionalNotationDuration = #(ly:make-moment 1/40)
\override Beam.grow-direction = #RIGHT
\featherDurations #(ly:make-moment 2/3)
{ e32[
\override NoteHead.transparent = ##t
e e e e e e e e e e e e e e]
}
%%%% 'proportionalNotationDuration' has no effect here (bug?):
\override Beam.grow-direction = #LEFT
{ e32[ e e e e e e e e e e e
\revert NoteHead.transparent
e]
}
\override Beam.grow-direction = #'()
s8
}