This isn't specifically an nginx question but as the forum is served via nginx it could be.

When I search the forum for "perl variable" it returns a '502 Bad Gateway' response and
the version 'nginx/0.8.5'. This happens every time I try the search but not for other terms.

Hello,

That was inappropriate to post to the nginx mailing list!

The problem was likely a timeout at your end as there were five results when I just ran that search.

--
Jim Ohlstein