Documentation on collision resolution

[Philip Potter]

I'm confused by the docs for collision resolution:

http://lilypond.org/doc/v2.12/Documentation/user/lilypond/Multiple-voices#Multiple-voices

In the example, the c2 and c8 are not merged because they have
different note-heads. But in the second bar, the e2 and e8 *are*
merged, despite having different note-heads. Worse, they are given a
filled note-head, not an open minim-style notehead. I tried it out on
my install (2.12.2) and got the same result as the example. What
causes this seeming inconsistency? Why is one merged and the other
not?

Phil