[Zope] Zope large-file-threshold

Hello, i'm trying to upload a large file (90Mb) via a web form. While doing so I expect Zope writing a temporary file into /tmp because the request is large than 'large-file-threshold' in zope.conf. But it all gets loaded into memory and no file ist created in /tmp. Am I missing something ? My Setup ist Zope-2.7.5 and Python 2.3.5 Regards Joern