Network Service Order not working properly.

Question

In System->Network->Set Service Order I have Thunderbolt Ethernet above Wi-Fi but this order doesn't seem to always be honoured.
Sometimes, it will use Wi-Fi even when TB Ethernet is connected and working.
OS X 10.8.5 on a 15" mid-2012 rMBP
Any ideas why? Known bug?
Annoying when doing things like back-ups as Gigabit Ethernet is faster than 802.11n

Answer 1

OK, after a couple of hours trawling through numerous threads about the TB->Ethernet adaptor I've found the answer. It's not a network problem per se, it's to do with the way network shares bind to network interfaces.
When a share mounts it searches for a network interface using the Service Order. As this is a laptop it invariably uses Wi-Fi as the TBE is usually not available. However, if a higher priority interface later becomes available, the share doesn't re-bind to this, it remains bound to the original interface.
The share will only bind to the new interface if either it is unmounted/remounted or the original interface goes away. So by turning off Wi-Fi it forces it onto the TBE (and Wi-Fi could be turned back on straightaway).
This also explains why, when I deleted the plist file you suggested, it appeared to work at first but this was only because the TBE was connected when I restarted my computer.
I don't know whether this is considered "standard" or "normal" behaviour for a network share or whether it's a bug - or just poor design - by Apple. As a user, i would want network activity to always use the fastest interface available.