(Answer: I'm the closest there is and I have no knowledge of how it
      works. The NCR driver is a lump of !@#$.)
      
Aarg, bad news here -- this problem seems to occur only when there
is NFS traffic, namely the source archive being copied was coming
from an NFS partition and being written to the disk.  While the NCR
driver needs a better restart policy, there might be a more systemic
issue to ponder out there....  This seems the sort of detail one ought
to share, although I don't expect any pat solutions.