second voice note has no flags

[Jay Hamilton]

In the example below the 16th note a should have two flags but has none and 
looks like a quarter note.
What did I do wrong this time?

\version "2.10.25"
melody = \relative c'
{
\clef treble
\key c \major
\time 3/4
#(set-global-staff-size 20)
\override Staff.TimeSignature #' style = #' ()
\override Staff.NoteCollision #'merge-differently-headed = ##t
\override Staff.NoteCollision #'merge-differently-dotted = ##t
<<
{
a16-p e''^\markup {a} dis-1-m cis-3-i e^\markup {a} dis-m cis-i a-4-p 
dis^\markup {a} cis-m a-i a,-p
\bar "|."
}
\\
{
a2 \hideNotes a8. \unHideNotes a16
}
>>

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



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Jay Hamilton
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