Why doesn't git-rerere automatically commit a resolution?

[Shawn Pearce <spearce@spearce.org>]

I'm curious... I have a pair of topic branches which don't merge
together cleanly by recursive (due to conflicting hunks in the
same line segments).  I enabled git-rerere, ran the merge, fixed
up the hunks and committed it.  git-rerere built its cache, as
the next time I pulled the two topic branches together and got
the same conflicts it correctly regenerated the prior resolution
(and printed a message saying as much).

But it git-rerere left the files unmerged in the index and it
doesn't generate a commit for the merge, even though there are no
merge conflicts remaining.  I expected it to update the index (to
merge the stages) and to generate a commit if possible; especially
in this case as I was pulling the exact same two commits together
again with the exact same merge base commit.

So I'm wondering why doesn't it try to finish the merge?  Was there
a really deep rooted reason behind it or was it simply easier/safer
to let the user sort out the working directory state every time?

-- 
Shawn.