Login disappears intermittently when going from page to page

I'm having a hard time nailing down the precise source of this problem, so if this is not an LDAP issue, my apologies.

We've been using LDAP for our intranet (just officially launched a couple weeks ago), and for the most part it is working well.

What's happening is that when somebody is logged in, sometimes when they go to another page, their login drops, and they become an anonymous user... just for that page. If they go on to another page, everything is fine, but if they return to a glitching page (often the home page), the login goes away again.

I'm not sure if the session is being lost or if this is a caching issue. I've turned off caching on the site, and the problem goes away, but not having caching is not feasible. That doesn't really make sense anyhow, because my understanding is that Drupal doesn't do caching during an authenticated session.

So, I've also tried turning off the LDAP module (while caching is still on): that also seems to fix the problem.

It's really quite odd, and if you have any suggestions on information I can gather or things I can do to help narrow this problem down, I'd be glad to do so.

Thanks!