openrsync errors using -x or --exclude

I am using rsync to back up files from a Linux box to an OpenBSD box,
i.e. from Samba rsync to openrsync. I run it so:

    linux$ rsync --rsync-path=openrsync -a -v $HOME/ openbsd-host:/path

Options -x/--one-file-system and --exclude give me errors on the
receiver end.

-x:
    openrsync: error: .: stat: No such file or directory
    rsync: connection unexpectedly closed (0 bytes received so far) [sender]
    rsync error: error in rsync protocol data stream (code 12) at io.c(232) [sender=3.4.1]

--exclude=/.cache/:
    openrsync: syntax error in received rules
    rsync: [sender] write error: Broken pipe (32)
    rsync error: error in socket IO (code 10) at io.c(849) [sender=3.4.1]

Is it a known problem? Workaround-able?

(I might have to install Samba rsync from the ports, but I'd like to use
openrsync from base if possible.)

Versions:
-   Linux Samba rsync v3.4.1 protocol v32
-   OpenBSD-current openrsync v0.1 protocol v27