Symantec's compate guide only mentions ML4 showing some issues...
ftp://exftpp.symantec.com/pub/support/products/NetBackup_Enterprise_Server/325328.pdf
If working on AIX version change is not easy/possible, try looking at debug log.
Enable nbjm/nbpem/bpbrm logs and increase verbose level, run the job, review it using vxlogview command and check out /usr/openv/netbackup/logs/bpbrm directory.
Interesting - are other multiple-stream jobs running ok?
Hot catalog backup job (especially the part where the job wraps up) is not any more than a simple multiple stream backup job...
Abe