\version "2.18.2"

%%% Problem both with merging noteheads AND with accidentals 

\language "english" 

\relative c' {         
\clef treble
\key bf \major
\time 2/4
<< 
  \voiceOne
  { 
  e'8. r16 a,!8. r16 |
  } 
   \\
   \new Voice
   \voiceTwo
{ 
  ef'!8. r16 af,8 gf16 r |
} 
>>
}