How to manage this workflow? (reloaded)

Hello,

I have two subversion repositories which I would like to synchronize via
git-svn.  For this, I have set up a git repository and configured two
branches to track the subversion repositories via git-svn:

    mkdir test-sync
    cd    test-sync
    git svn init --stdlayout file://$REPOSDIR/svn-first

    for repos in svn-first svn-second; do
        git config svn-remote.$repos.url      file://$REPOSDIR/$repos
        git config svn-remote.$repos.fetch    trunk:refs/remotes/$repos/trunk
        git config svn-remote.$repos.branches branches/*:refs/remotes/$repos/*
        git config svn-remote.$repos.tags     tags/*:refs/remotes/$repos/tags/*
        git svn fetch -R $repos
        git checkout -b $repos $repos/trunk
    done
    git gc

This gives me two remote and two local branches:

    master
    svn-first
  * svn-second
    svn-first/trunk
    svn-second/trunk

As a first step, I tried to "mirror" the manual "merges" that were done
between the subversion repositories in the past:

    git checkout svn-first
    git cherry-pick svn-second-sha1 .... # repeat as needed

    git checkout svn-second
    git cherry-pick svn-first-sha1 .... # repeat as needed

So I've spent almost 4 weeks to cherry-pick and resolve all the conflicts.
Looks good so far, since

    git diff svn-first svn-second
    git diff svn-first/trunk svn-first/trunk
    git diff svn-second/trunk svn-second/trunk

give me the desired outputs.  Now I do

    git checkout svn-first
    git merge -s ours svn-second
    git checkout svn-second
    git merge -s ours svn-first

to tell git that the branches are in sync.

But now, when I try to

    git checkout svn-second
    git svn rebase

I get lots of conflicts.  When I inspect the .git/rebase-apply directory
and the conflicts, it looks like "git svn rebase" tries to re-apply all
the commits from svn-first.  When I omit the "git merge -s ours svn-first"
command, it does not re-apply those commits.  So it looks like the
"git merge -s ours" wipes some information that git-svn needs to know
what was already merged.

What am I missing?  I thought the "ours" strategy is meant to tell git
that everything from that branch was merged, either manually or by
cherry-pick.

Any hints how to track this down?

BTW: this is git version 1.6.0.2