Error message in log.nmbd on NEW server: workgroup search for OLDDOMAIN fails ... workgroup name OLDDOMAINxxxxxxxxy with is too long. (x=space, y=0x1b)
Debug level 4 shows failure in source/nmbd/nmbd_workgroupdb.c
It appears that, having found the domain master record received from OLD server, the 0x1b is incorrectly included in the returned domain name.
There is no reciprocal error in OLD server's log.nmbd.
This might affect synchronisation of credentials, but I have not established that.