[Zope] File upload - form doesn't empty the "file" field

Hello, I know this might be a HTML question but I'm not very experienced in file uploads. So please bear with me. I have created a form which - among other - uploads a file to the filesystem. That works. But when I go back to the upload page, updates some attributes and submit the data, the data that comes back contains the file that I uploaded the last time. The file attribute of the request isn't being emty. Do I have to set VALUE="" at the input field ??? Anyone with a good idea ? Regards,