Unfortunately you have hit one of the limitations with the current DSpace SWORD implementations. Due to the way DSpace currently works, it does not generate an item handle until the item has completed its journey through the workflow(s). And to compound this problem, the media link will not return anything for items that are due to go through a workflow. It is probably worth submitting this as a bug in JIRA (jira.dspace.org) so that we can assess it for future releases. The first of these issues (and therefore the second too) may get fixed in 1.6 if we can find the effort required to port some previous work on the identifier system to 1.6 to ensure that all items are given item identifiers. If this work does not get incoroporated in 1.6, we could look at adding a new DSpace table to associate a new SWORD deposit ID with the final ID and return that to the user via the media link.
T. Strohman, W. Croft, und D. Jensen. Proceedings of the 30th annual international ACM SIGIR conference on Research and development in information retrieval, Seite 705--706. New York, NY, USA, ACM, (2007)