You encounter this problem only when the first connection from a client to the ePO server takes place over a VPN connection.
NOTE: If the computer's first connection is via a Local Area Network (LAN), the correct Media Access Control (MAC) address is added to the table.
When a computer communicates with the ePO server via VPN, it uses the VPN virtual computer's MAC address and not its own actual MAC address. This VPN MAC address is usually the same for all computers connecting through the VPN.
This issue isn't restricted only to VPN clients. Anything that can cause multiple computers to report the same MAC address can cause this problem. For example, if you clone a virtual machine and don't reset the MAC address, both computers report the same MAC address to ePO.