Funny thing is, I get these "502 bad gateway" errors *all the time* with this site (not on specific URLs like the OP, just generally). By that I mean that I run into them at least 3-4 times/year, and usually when I do, the forums are unusable and I just have to come back in several hours or a day. I don't think I have ever encountered a similar error on any other web site. So all this stuff about cookies, caches, proxies, etc. is interesting, but clearly there is something weird about eevblog.
Maybe it's Oz... left-handed vs right-handed electrons in the southern hemisphere?