seoskunk - 7:09 pm on Apr 29, 2013 (gmt 0)
I don't know why for certain some sites are affected by proxies more than others but I would guess it being some sort of trust issue.
Its very frustrating to have to deal with this and you have my sympathy turbocharged and I strongly suggest you try forward reverse dns of googlebot as a solution to the problem.
I fail to see why google can't eliminate this from the web, especially if its their own properties. I guess they have there reasons and may feel the site in some way deserves it.