Issue met when invoking these operations in CLI:

/server-group=main-server-group:write-attribute(name="socket-binding-port-offset", value=100)
/host=master/server-config=server-one:restart
/server-group=main-server-group:write-attribute(name="socket-binding-port-offset", value=0)
{
"outcome" => "failed",
"failure-description" =>

{"domain-failure-description" => "0 is an invalid value for parameter socket-binding-port-offset. A minimum value of 1 is required"}

,
"rolled-back" => true
}

In standard distribution there is no port offset defined for /server-group=main-server-group.

Tested with latest build from source codes pulled on 2011-10-18.