Comment # 43 on bug 1007695 from Michal Marek

Can you provide 'dmidecode' output from the system? It should list something
like:

Handle 0x2900, DMI type 41, 11 bytes
Onboard Device
        Reference Designation: Embedded NIC 1
        Type: Ethernet
        Status: Enabled
        Type Instance: 1
        Bus Address: 0000:02:00.0

Handle 0x2901, DMI type 41, 11 bytes
Onboard Device
        Reference Designation: Embedded NIC 2
        Type: Ethernet
        Status: Enabled
        Type Instance: 2
        Bus Address: 0000:02:00.1

...

I.e. different type Instance values for devices of the same type.