stem choice bug with simultaneous expressions

[David Tresner-Kirsch]

> I'm not top posting.

% In simultaneous expressions within a voice, if a note in the first written 
expression begins at the same time as a shorter note in another written 
expression, the two notes sometimes incorrectly share the stem type of the 
first.

% This example should appear to readers as having a total length of one 
eighth. Instead it shows up as an eighth chord followed by an additional 
sixteenth.
\version "2.16.2"

\new Voice {<< {c8} { e16 f16} >>}