Creating a new version of an item results in a null/undetected bitstream format once the upload step for the new version is reached.
In JSPUI, the bitstream format for each file (no matter what the previous format) will say "Unknown". In XMLUI it will say application/octet-stream.
Perhaps something to do with how the bitstreams are re-submitted/re-registered?
I have not investigated this closely yet, or tested against previous releases of DSpace.