bmi diamond club - US Go cash upgrades

Having nosed about in the M&M forum I noticed they credit C class miles for US cash upgrades (http://www.flyertalk.com/forum/miles-more-lufthansa-austrian-swiss-other-partners/910007-us-airways-gate-paid-cash-upgrade.html) (Go Upgrades). Now I have used the go upgrade couple of times and always assumed miles will be credited in the underlying Y class fare.

Has anyone ever got DC to credit C class miles when using a cash upgrade?:confused:

I did a Go upgrade (albeit 18 months ago) for Envoy and it credited Y miles. I had a cheeky send in of the boarding card, but US confirmed the economy fare and that I had a paid upgrade that didn't earn miles.

Not sure if they have had a change of policy since then though.

Pretty much the same a year ago from Y (T fare) to Envoy for a friend. Only Economy miles given.

The same if you buy-up or get a battlefield upgrade on UA - Underlying fare class is what counts...