strange appoggiatura behaviour

[James E. Bailey]

Oddly, in the attached code, if the appoggiatura is commented out,  
then the stems follow how they're supposed to. Is this a bug or a  
super-special feature of graceMusic that I just didn't know about?

\version "2.11.57"
{
   \relative {
      \voiceOne
      \appoggiatura e'
      f4 e d c b a g f
   }
}