Allied Telesis AT-S62 - Manual (Page 450)

Chapter 22: Multiple VLAN Modes
Section V: Virtual LANs 450
Another difference with this mode is that the uplink port is untagged.
Consequently, you would want to use this mode when the device
connected to the uplink port is not IEEE 802.1Q compatible, meaning
that the device cannot handle tagged packets.
Note
When the uplink port receives a packet with a destination MAC
address that is not in the MAC address table, the port will broadcast
the packet to all switch ports. This can result in ports receiving
packets that are not intended for them.
It should also be noted that a switch operating in this mode can be
remotely managed through any port on the switch, not just the
uplink port.