That dbus chown does the trick, thanks.
Now, there is the keyboard problem, I think you have the n800 plus BT kbd so you don't see it, but with the n810 only first function chars do work, not 2nd function (blue) chars. This happens only inside a Xephyr window.
Must be some specific keyboard config to be copied between the maemo root and the debian chroot. Unfortunately at present I have no clue where to look for.

By the way, JWM is really cool, very minimalist and quick. Try it...