Allied Telesis AT-S39 - Manual (Page 301)

AT-S39 User’s Guide
301
Note
Ports designated as untagged ports of the new VLAN are
automatically removed from their current untagged VLAN
assignment. For example, if you are creating a new VLAN on a switch
that contains only the Default_VLAN, the ports that you specify as
untagged ports of the new VLAN are automatically removed from
the Default_VLAN.
Tagged ports are not removed from any current VLAN assignments
because tagged ports can belong to more than one VLAN at a time.
The new VLAN is now ready for network operations.