Is there a known problem with Drupal losing/corrupting SESSION variables for anonymous users when caching is active?
If there is, could someone point me to some detailed info? I've searched around quite a bit and found scattered reports of people struggling to control this kind of SESSION data for anonymous users unsuccessfully, but I'm unable to find anything that conclusively explains why this is so.
Situation is this:
Anonymous users may hit about 600 course pages, all of which have a link to one of two department-specific webforms for submitting inquiries; we need to save info on the page users hit the webforms from so we can redirect them back to the originating page from the confirmation screen (after form submission), and so that we can send mail tagged with the specific course page an inquiry originated from.
When Boost caching is active for these pages, we sometimes to most of the time lose parts of the path information needed for correct redirection to the confirmation page and give a 404 error instead (we can see from log data that the page being directed to is a non-existent page, based on its URL having been specified minus some of the needed path info); when we exclude these forms and course pages from caching, with no other changes, this problem does not occur at all.
For the moment, turning caching off for these pages is having little obvious effect on the speed site pages load, but it doesn't seem like much of a solution since to get these form features to work, we've had to specify that 600 or more pages of a site total of about 850 not be cached.
Is there something obvious I'm missing here? We've been able to test in a staging environment and not see these SESSION corruptions, but then once the same caching is live on the production site, the problem comes right back. I assume it's related to the number of simultaneous users of the forms, but I thought that was the whole point of a session, to preserve state for a (potentially) anonymous user across a set of pages.