FreeBSD 8.1-PRERELEASE: property 'jailed' not supported on FreeBSD: permission denied

[Eugene Mitrofanov]

Hi

The command "zfs set jailed=on tank/s1" is failed with the message "
property 'jailed' not supported on FreeBSD: permission denied".

Output of "zfs get jailed tank/s1" shows me that the property "jailed" is 
still exists:
NAME     PROPERTY  VALUE    SOURCE
tank/s1  jailed    off      default

How can I change its value?

Thanks.
-- 
EMIT-RIPN, EVM7-RIPE