this sounds like the typical difference shown between IE and Netscape when viewing text/plain files. for some reason, IE ignores the content-type and shows many text/plain pages as if they are text/html. combined with what tye said, i would guess that a transparent proxy is caching perlmonks.org, but is not sending it out with the original MIME type (using text/plain instead since the extension is .pl, not .html). IE's erroneous behavior makes it seem like nothing is wrong, whereas Netscape and Konqueror are both acting correctly on the text/plain MIME type.

if you have LWP installed, use the HEAD program to fetch the HTTP headers for the page in question to be sure.