Can you please give a try to create two DIRs with different document type and provide same document no to them? System will allow to create it.
Note: No range in both doc type must be similar.
That is why system ask to enter doc type in CV03N and In CV04n, if you dunno enter doc type but only doc no then it will result you the list of all document with same doc no and different doc type. So in CV04N doc type is not mandatory as it is a report not only individual doc display.