When adding a file by POSTing it to the EM-IRI of an existing item in DSpace, the bitstream doesn't seem to be given a file type, so it classified as 'unknown'.
However, the same files added to the SWORD bundle, are given their correct file types.
Screen shot attached, or see example at http://93.93.131.168:8080/jspui/handle/123456789/40
