Major Description
When using the @EventListener, the client usually stuffs a beventtarget.id parameter into the request to indicate which browser event the user has triggered.
Somehow, the beventtarget.id parameter doesn't make it into the request for multipart forms (i.e. when the request contains an Upload component).
I tried debugging this on the server-side, but it looks like a client-side issue since the Multipart decoder isn't finding the parameter in the servlet request at all.