pushing over hpss ignores stacking policy

Again, I attempt to make myself precise with a transcript:

$ cd ~/tmp
$ rm -rf repro
$ mkdir repro
$ cd repro
$ bzr init-repo --development repo
$ bzr init --development repo/base
$ echo "default_stack_on=$(pwd)/repo/base" > repo/.bzr/control.conf
$ bzr init --development to-push
$ bzr push -d to-push repo/push1
Using default stacking branch /home/mwh/tmp/repro/repo/base at file:///home/mwh/tmp/repro/repo/
Created new branch.
$ cat repo/push1/.bzr/branch/branch.conf
stacked_on_location = /home/mwh/tmp/repro/repo/base
$ bzr serve --allow-writes &
[1] 29280
$ sleep 1 # to let the server start up
listening on port: 4155
$ bzr push -d to-push bzr://localhost/repo/push2
Created new branch.
$ cat repo/push2/.bzr/branch/branch.conf
$