PHPSESSID invalid input tag

Hi there,
Recently, I believe my host may have changed its PHP.ini configuration files, and now with any forms (on pages powered by WordPress) PHP forces a hidden <input> tag into the form, but in the wrong place, breaking all validity XHTML. My host says they wont be able to change the PHP.ini on my request, and recommend I either look for an alternative way-around for the problem or ignore it. Has anyone else had this problem? Does anyone have any workarounds? Thankyou very much!
Steve