> \partCombine #'(1 . 1)
> { \aikenHeads f'2 }
> { \aikenHeads f'2 }
This is an interesting problem. LilyPond's Emmentaler font contains
two shapes of this glyph, namely `noteheads.d1fa` and
`noteheads.u1fa`, where the 'd' and 'u' stands for 'down' and 'up',
respectively (you can see the glyphs in Appendix A.8 of the Notation
Reference). It seems that the part combine engine uses the 'down'
version of the glyph if two voices fall together; AFAIK, this is an
arbitrary choice without a possibility to adjust.
I have no idea how the part combiner works, but it shouldn't be too
hard to add a property to select which shape should be used in this
case.
If my analysis is correct, I suggest to open an issue in our tracker.
Werner
