Consider following situation: first FS is mounted into /mount and second into /mount/fs2. In Zabbix was set up fs discovery with a few items vfs.fs.size[fs, free|total|pused]. Filesystems are discovered correctly,where first fs in /mount has all items supported,but second fs in /mount/fs2 claims 'Not supported' of all associated items. Tested on HPUX,AIX,Linux with same results.
Some debbug from agent log:
2187270:20130314:175543.870 Processing request.
2187270:20130314:175544.033 Requested [vfs.fs.size[/mount/fs2,free]]
2187270:20130314:175544.033 Sending back [ZBX_NOTSUPPORTED]
2191392:20130314:175544.063 In send_buffer() host:'zabbix_server.domain.cz'
port:10051 values:0/100
2191392:20130314:175544.063 End of send_buffer():SUCCEED
2191392:20130314:175544.063 Sleeping for 1 second(s)

Thank you