Ivan,
It's a bit hard to say exactly what is going on here as we probably need a bit more info....
but I'll hazard some guesses.
Firstly, I don't know of anything in recent jetty releases that would send a 302 response to a multipart POST, so if the 302 being sent is new, then I don't think it is jetty that is sending it.
It is correct that a new request after a 302 should be a GET, but technically speaking a GET should not include a message body. We've never really agreed with that part of the spec and Jetty is typically happy to accept a GET with a body. However, you may wish to review your client and/or design if it really relies on this, as I'm pretty sure it is not required to be supported.
But looking at the image supplied, it does appear that a GET request is eventually generated that has the multipart content.
So how are you doing the file upload? MultipartFilter? Servlet 3.1 Part API? ServletRequest.getParameter?
You could try adding POST to the methods that support form content in HttpConfigurationClass, but I'm not entirely sure that will help... but I'm guess there is some kind of method switch in the path that needs to be configured. Tell us what the path is and we can tell you more.
cheers