If a forward is executed at some point during a multipart submit/request, the multipart filter is triggered again and tries to re-parse the already parsed request. The multipart filter (both the cos one and the commons-fileupload one) should extend OncePerRequestFilter and not simply the AbstractMagnoliaFilter.

Steps to reproduce:

• create a page with a multipart form and a file upload input.
• make the form submit to a virtualUri
• make that virtualUri do a forward (not redirect) to another page
• submit the form with a file
• see the exception

This is the simplest case (even if not common, I admit). But any forward on multipart request causes the same problem.