problems with pdf download

I have searched and searched, but I can't find any references to this issue. When I use a GET method on a form to a dynamic pdf generator, it works perfectly, but if I use a POST method, I get a "This page contains both secure and non-secure information..." message. Does anyone out there know of any bugs in IE that would make it respond like this? Has anybody ever heard of such a problem? This has got to be a common occurance (downloading a pdf created with POST vars).... I don't think that it is a PHP issue, but I post here just in case. Thanks. Pete.