I tried the "push -r 1 --overwrite" trick with bzr-svn 0.5 RC1 and it doesn't work:
bzr push -r 1 -v --overwrite svn+http://localhost/svn/test/trunk/gui

The svn+ syntax is deprecated, use http://localhost/svn/test/trunk/gui instead.
Initialising Subversion metadata cache in /home/enigma/.bazaar/svn-cache/27530666-c0bc-4525-b9dd-495b6ed8d586
Upgrade to Subversion 1.5 or higher for faster retrieving of revision properties.
bzr: ERROR: exceptions.AssertionError: revprops: ['bzr:revision-id', 'bzr:user-agent', 'bzr:timestamp', 'bzr:root', 'bzr:committer', 'svn:log', 'bzr:revprop:branch-nick', 'bzr:file-ids', 'bzr:base-revision', 'bzr:revno', 'bzr:mapping-version']

Traceback (most recent call last):
  File "/usr/lib/python2.5/site-packages/bzrlib/commands.py", line 893, in run_bzr_catch_errors
    return run_bzr(argv)
  File "/usr/lib/python2.5/site-packages/bzrlib/commands.py", line 839, in run_bzr
    ret = run(*run_argv)
  File "/usr/lib/python2.5/site-packages/bzrlib/commands.py", line 539, in run_argv_aliases
    return self.run(**all_cmd_args)
  File "/usr/lib/python2.5/site-packages/bzrlib/builtins.py", line 913, in run
    use_existing_dir=use_existing_dir)
  File "/usr/lib/python2.5/site-packages/bzrlib/push.py", line 162, in _show_push_branch
    stop_revision=revision_id)
  File "/usr/lib/python2.5/site-packages/bzrlib/decorators.py", line 138, in read_locked
    result = unbound(self, *args, **kwargs)
  File "/usr/lib/python2.5/site-packages/bzrlib/branch.py", line 1799, in push
    _override_hook_source_branch=_override_hook_source_branch)
  File "/usr/lib/python2.5/site-packages/bzrlib/branch.py", line 2508, in _run_with_write_locked_target
    result = callable(*args, **kwargs)
  File "/usr/lib/python2.5/site-packages/bzrlib/branch.py", line 1838, in _push_with_bound_branches
    result = self._basic_push(target, overwrite, stop_revision)
  File "/usr/lib/python2.5/site-packages/bzrlib/branch.py", line 1861, in _basic_push
    graph=graph)
  File "/home/enigma/.bazaar/plugins/svn/branch.py", line 458, in update_revisions
    _push_merged, _override_svn_revprops)
  File "/home/enigma/.bazaar/plugins/svn/branch.py", line 479, in _push_missing_revisions
    override_svn_revprops=_override_svn_revprops)
  File "/home/enigma/.bazaar/plugins/svn/commit.py", line 986, in push
    override_svn_revprops=override_svn_revprops)
  File "/home/enigma/.bazaar/plugins/svn/commit.py", line 944, in push_revision_tree
    revid = builder.commit(rev.message)
  File "/home/enigma/.bazaar/plugins/svn/commit.py", line 591, in commit
    "revprops: %r" % self._svn_revprops.keys()
AssertionError: revprops: ['bzr:revision-id', 'bzr:user-agent', 'bzr:timestamp', 'bzr:root', 'bzr:committer', 'svn:log', 'bzr:revprop:branch-nick', 'bzr:file-ids', 'bzr:base-revision', 'bzr:revno', 'bzr:mapping-version']

bzr 1.10 on python 2.5.2 (linux2)
arguments: ['/usr/bin/bzr', 'push', '-r', '1', '-v', '--overwrite', 'svn+http://localhost/svn/test/trunk/gui']
encoding: 'UTF-8', fsenc: 'UTF-8', lang: 'en_US.UTF-8'
plugins:
  bzrtools             /usr/lib/python2.5/site-packages/bzrlib/plugins/bzrtools [1.10]
  gtk                  /usr/lib/python2.5/site-packages/bzrlib/plugins/gtk [0.95.0.final.1]
  launchpad            /usr/lib/python2.5/site-packages/bzrlib/plugins/launchpad [unknown]
  rebase               /home/enigma/.bazaar/plugins/rebase [0.4dev]
  svn                  /home/enigma/.bazaar/plugins/svn [0.5.0.rc.1]
*** Bazaar has encountered an internal error.
    Please report a bug at https://bugs.launchpad.net/bzr/+filebug
    including this traceback, and a description of what you
    were doing when the error occurred.