Looks like the request composed by info.magnolia.module.exchangesimple.Transporter doesn't actually follow standards (header separator missing), this causes a MalformedStreamException when the activation request is parsed by commons-fileupload:

org.apache.commons.fileupload.MultipartStream$MalformedStreamException: Stream ended unexpectedly
at org.apache.commons.fileupload.MultipartStream.readHeaders(MultipartStream.java:542)
at org.apache.commons.fileupload.FileUploadBase$FileItemIteratorImpl.findNextItem(FileUploadBase.java:859)
at org.apache.commons.fileupload.FileUploadBase$FileItemIteratorImpl.hasNext(FileUploadBase.java:916)
at org.apache.commons.fileupload.FileUploadBase.parseRequest(FileUploadBase.java:348)
at org.apache.commons.fileupload.servlet.ServletFileUpload.parseRequest(ServletFileUpload.java:126)
at info.magnolia.cms.filters.MultipartRequestFilter.parseRequest(MultipartRequestFilter.java:132)
at info.magnolia.cms.filters.MultipartRequestFilter.doFilter(MultipartRequestFilter.java:105)
at info.magnolia.cms.filters.AbstractMagnoliaFilter.doFilter(AbstractMagnoliaFilter.java:46)
at info.magnolia.cms.filters.MagnoliaFilterChain.doFilter(MagnoliaFilterChain.java:48)
at info.magnolia.cms.security.BaseSecurityFilter.doFilter(BaseSecurityFilter.java:39)
at info.magnolia.cms.filters.AbstractMagnoliaFilter.doFilter(AbstractMagnoliaFilter.java:46)
at info.magnolia.cms.filters.MagnoliaFilterChain.doFilter(MagnoliaFilterChain.java:48)
at info.magnolia.cms.security.LogoutFilter.doFilter(LogoutFilter.java:63)
at info.magnolia.cms.filters.OncePerRequestAbstractMagnoliaFilter.doFilter(OncePerRequestAbstractMagnoliaFilter.java:29)
at info.magnolia.cms.filters.MagnoliaFilterChain.doFilter(MagnoliaFilterChain.java:48)
at info.magnolia.cms.security.auth.login.LoginFilter.doFilter(LoginFilter.java:72)
at info.magnolia.cms.filters.AbstractMagnoliaFilter.doFilter(AbstractMagnoliaFilter.java:46)
at info.magnolia.cms.filters.MagnoliaFilterChain.doFilter(MagnoliaFilterChain.java:48)
at info.magnolia.cms.filters.ContentTypeFilter.doFilter(ContentTypeFilter.java:60)
at info.magnolia.cms.filters.AbstractMagnoliaFilter.doFilter(AbstractMagnoliaFilter.java:46)
at info.magnolia.cms.filters.MagnoliaFilterChain.doFilter(MagnoliaFilterChain.java:48)
at info.magnolia.cms.filters.MgnlContextFilter.doFilter(MgnlContextFilter.java:83)
at info.magnolia.cms.filters.AbstractMagnoliaFilter.doFilter(AbstractMagnoliaFilter.java:46)
at info.magnolia.cms.filters.MagnoliaFilterChain.doFilter(MagnoliaFilterChain.java:48)
at info.magnolia.cms.filters.MagnoliaMainFilter.doFilter(MagnoliaMainFilter.java:116)
at info.magnolia.cms.filters.AbstractMagnoliaFilter.doFilter(AbstractMagnoliaFilter.java:46)