Hi Hwaen,
The single notes and triads merge correctly, but the
four-note chords do not.
This seems to be a bug. The culprit is the combination of two notes a
step apart (and you can see that they are aligned differently in both
instances).
While I can't provide you with a solution right now, maybe the following
minimal example helps:
\version "2.20.0"
\new Staff \fixed c'
<<
{ <f a> <g a> <g b> } \\
{ <f a> <g a> <g b> }
>>
Lukas
PS. As an aside: To be honest, I think that the triple-dots in the
lowest voice, while perfectly correct, are overkill. Of course it's a
matter of style and taste, but my feeling is that lots of composers
(like Schumann for instance) would just have written a downwards stem
without bothering to much about the mathematically correct length.
