We have many nested mount points on our servers,but these can't be monitored, because they keep in state Not supported.
Brief explanation of this behavior:
First FS is mounted into /mount and second into /mount/fs2. In Zabbix the server has items vfs.fs.size[fs, free|total|pused] for these two FS. First fs in /mount has all items supported,but second fs in /mount/fs2 claims 'Not supported' on all associated items. Tested on HPUX,AIX,Linux with same results.

Some debug from agent log:
Processing request.
Requested [vfs.fs.size[/mount/fs2,free]]
Sending back [ZBX_NOTSUPPORTED]
In send_buffer() host:'zabbix_server.domain.cz'
port:10051 values:0/100
End of send_buffer():SUCCEED
Sleeping for 1 second(s)

Thank you