git-svn and branches

I'm using git-svn to track a rather large subversion repository with a
non-standard layout.  In the past, I've only cared about trunk, but now
I need to occasionally use branches, too.  By adding a second git-svn
remote with the branch URL, I can fetch the branch, and git-svn is even
intelligent enough to notice that the branch was copied off of trunk.

However, git-svn also does a complete checkout for the first revision of
the branch.  By this, I mean it goes through shows "A    file" for every
file in the repository.  This takes quite a while, and seems rather
unnecessary given that git-svn already noticed that the branch shares a
history with trunk, which is already fetched.

Knowing just enough of what git-svn is doing to be dangerous, I whipped
up a short little patch.  This patch seems to work for the common case,
and avoids fetching every file from subversion.  It does break
sometimes, however, and I don't understand why.

Maybe someone with a better grasps of the code can see what I did wrong,
or suggest a better means to my end?

diff --git a/git-svn.perl b/git-svn.perl
index 484b057..1bc92b6 100755
--- a/git-svn.perl
+++ b/git-svn.perl

@@ -1848,9 +1848,10 @@ sub find_parent_branch {
                                              $self->full_url, $ed)
                          or die "SVN connection failed somewhere...\n";
                } else {
+                       $self->assert_index_clean($parent);
                        print STDERR "Following parent with do_update\n";
                        $ed = SVN::Git::Fetcher->new($self);
-                       $self->ra->gs_do_update($rev, $rev, $self, $ed)
+                       $self->ra->gs_do_update($rev, $r0, $self, $ed)
                          or die "SVN connection failed somewhere...\n";
                }
                print STDERR "Successfully followed parent\n";

-- 
-Steven Walter <stevenrwalter@gmail.com>
"A human being should be able to change a diaper, plan an invasion,
butcher a hog, conn a ship, design a building, write a sonnet, balance
accounts, build a wall, set a bone, comfort the dying, take orders,
give orders, cooperate, act alone, solve equations, analyze a new
problem, pitch manure, program a computer, cook a tasty meal, fight
efficiently, die gallantly. Specialization is for insects."
   -Robert Heinlein