merge with a merge directive in a lightweight checkout from a bzr+ssh:// branch fails

Create a repository containing a main branch, a derived feature branch:

bzr init-repository repo1
bzr init repo1/b1
echo foo >repo1/b1/f1
bzr add repo1/b1/f1
bzr commit repo1/b1/f1 -m 1
bzr branch repo1/b1 repo1/b2
echo bar>repo1/b2/f1
bzr commit repo1/b2/f1 -m 2

Create a merge directive for delivering the feature branch:

bzr send -o 2.patch -f repo1/b2 repo1/b1

Create another repository with a copy of the main branch and merge in a local
lightweight checkout:

bzr init-repository repo2
bzr branch repo1/b1 repo2/b1
bzr co --lightweight repo2/b1 checkout1
(cd checkout1 && bzr merge ../2.patch)

=> works fine: all changes applied successfully.

Now do the same using using a lightweight checkout through bzr+ssh:

bzr init-repository repo3
bzr branch repo1/b1 repo3/b1
bzr co --lightweight bzr+ssh://localhost/$PWD/repo3/b1 checkout2
(cd checkout2 && bzr merge ../2.patch)

=> bzr: ERROR: Branches have no common ancestor, and no merge base revision was specified.

Try a second time:

(cd checkout2 && bzr merge ../2.patch)

=> it works!