differently headed works for part but not all?

[Jay Hamilton]

In this example some of the notes are joined but not the 16ths and dotted 8ths  
Is this known? is there something I should be adding?
Jay

\version "2.10.25"

melody = \relative c'
{
\clef treble
\key c \major
\time 2/4
#(set-global-staff-size 22)
\override Staff.TimeSignature #' style = #' ()
\override Staff.NoteCollision #'merge-differently-headed = ##t
<< {
%line 2
c8 g'16 e' ~ e b g8
c, g'16 d ~ d f, a' a
g,8 b'16 ais ~ ais d, ais' ais
c,8 g'16 d ~ d f, a' a
\bar "|."
}
\\
{
%line 2
c,2 c8 r r16 f,8. g4 r16 d'8. c8 r r16 f,8.
}



>>

  }
\score {
\new Staff \melody
\layout { }
\midi { }
}




Jay Hamilton
www.soundand.com
206-328-7694