Shifted notehead won't merge with same pitch from other voice

[Javier Ruiz-Alma]

I'm typesetting the attached music using four voices.  However, a shifted quarter note refuses to merge with the half-note from other voice. I suspect it has to do with both having same stem direction, but how does one tell LP to merge anyway? Force-shifting notecolumn didn't seem to do the trick.

\version "2.18.2"

\relative c' {

\key g \minor

<<

{ \stemDown \hideNotes c8_~ \unHideNotes c2 }

\\

{ \stemUp c8[ d fis bes a] }

\\

{ \mergeDifferentlyHeadedOn \stemUp s8 d,2 }

\\

{ \mergeDifferentlyDottedOn s4 fis4. }

>>

}

MergeNoteheads.PNG
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