Collision between stem and accidental

[Federico Sarudiansky]

The following code shows the collision between a stem and an accidental (flat) 

\version "2.12.3"

\score {
  \relative c, { 
    \clef bass 
    <c aes''>4 \downbow 
    <c aes''>8. \downbow 
    <c aes''>16 \upbow  
    <aes' f'>2 \downbow 
    | }
}

however, using a sharp or a forced natural shows no collision. 

Hope it'd be useful, 

F.