Comment 10 for bug 1090002

You can see the same phenomenon in the tarball that Narinder posted above.

Here's the em3 definition at the time em1 appeared:
BIOS device: em3
Kernel name: em3
Permanent MAC: 00:17:A4:77:3C:08
Assigned MAC : 00:17:A4:77:3C:08
ifIndex: 4
Driver: be2net
Driver version: 4.2.220u
Firmware version: 4.1.450.7
Bus Info: 0000:04:00.2
PCI name : 0000:04:00.2
PCI Slot : embedded
Embedded Index: 3

And then at the time em2 appeared:
BIOS device: em3
Kernel name: em5
Permanent MAC: B4:99:BA:A6:B9:18
Assigned MAC : B4:99:BA:A6:B9:18
ifIndex: 6
Driver: be2net
Driver version: 4.2.220u
Firmware version: 4.1.450.7
Bus Info: 0000:04:00.4
PCI name : 0000:04:00.4
PCI Slot : embedded
SMBIOS Device Type: Ethernet
SMBIOS Instance: 5
Embedded Index: 5

As you can see above, the same BIOS entry "em3" switched mac address and now refers to a completely different NIC.