this is happening with both my thunderbolt display and thunderbolt<->ethernet adaptor....
the ether net in the t-bolt display WAS working.... but was having probs with the ethernet adaptor while on the road, so I tried deleting the thunderbolt ethernet entry from the Network Preferences panel. Well, now when I hook up my thunderbolt Display, the option doesn't re-appear! So now I'm thinking there's something in the system that's keeping that from re-appearing in the network preference panel, and it could be the reason for both items not working.
The controller is recognized at a low level by the system - in system report I get:
Type: Ethernet Controller
Slot: Thunderbolt Slot 2@11,0,0
Vendor ID: 0x14e4
Device ID: 0x16b0
Subsystem Vendor ID: 0x106b
Subsystem ID: 0x00f1
Revision ID: 0x0010
Link Width: x1
BSD name: en2
Kext name: AppleBCM5701Ethernet.kext
Firmware version: 57761-a1.48, 0x2fe676f9
Location: /System/Library/Extensions/IONetworkingFamily.kext/Contents/PlugIns/AppleB CM5701Ethernet.kext
mDNS offload capable: c8:2a:14:4f:a3:90
So it's a problem with the Network Preferences panel getting loaded, somehow. I tried re-creating the kext cache, that didn't help.
Digging around a little in the system, I see this:
But I'm out of ideas how to get the thunderbolt ethernet option back into the Network Preference panel. help?!