WWW prefix handling drops path

If I have WWW prefix handling enabled, direct navigation to a node (or any path) with a www. prefix drops the whole path and goes to the front page.

Live examples:

http://supportunitedway.org/youth/msti - works
http://www.supportunitedway.org/youth/msti - pops back to the homepage

On another server:

http://apexic.net/node/10 - works
http://www.apexic.net/node/10 - pops back to the homepage

In both cases, if I turn WWW prefix handling off, the second address works. I don't have any weird mod rewrites. I've got a wildcarded virtual server working. I will keep checking my server settings, but I wanted to see if anyone else had experienced this. That it is happening on two different servers makes me think it's a module thing. It's very odd to me since the only place I can see this gets applied is a simple bit of code in domain_init():

  if (variable_get('domain_www', 0)) {
    $_subdomain = str_replace('www.', '', $_subdomain);
  }