[Networker] Backup group starts, but never writes to AFTDs .. ?

Wondering if anyone else has run across this...

System is a Sun M2900, Solaris 10, Networker 7.5.1 (Sun "EBS"). It backs 
up itself to eleven AFTDs and clones (also stages) to three SDLT320 drives 
in a small autochanger. This has happened only twice in the last year, but 
it's been the exact same thing both times. The backup group kicks off 
normally and the usual nsr* processes appear, but /nothing/ ever happens 
on the disk backup volumes at all.

Looking at /nsr/logs/daemon.log, there are LOTS of entries like this:

    42506 09/16/10 21:17:24  nsrd write completion notice: Writing to 
volume XXX.001 completed
    11348 09/16/10 21:17:25  nsrd deactivating mmd #1
    67898 09/16/10 21:17:25  nsrd Calling mm_deactivate for mmd 1 that is 
using device /dbu/dev.001 with volume XXX.001 on host XXX
    11388 09/16/10 21:17:26  nsrd re-setting overall number of authorized 
save sessions, changing value from (1) to (0)
    11348 09/16/10 21:17:30  nsrd deactivating mmd #1
    67898 09/16/10 21:17:30  nsrd Calling mm_deactivate for mmd 1 that is 
using device /dbu/dev.001 with volume XXX.001 on host XXX
    42506 09/16/10 21:17:30  nsrd write completion notice: Writing to 
volume XXX.001 completed
    11348 09/16/10 21:17:31  nsrd deactivating mmd #1
    67898 09/16/10 21:17:31  nsrd Calling mm_deactivate for mmd 1 that is 
using device /dbu/dev.001 with volume XXX.001 on host XXX
    11388 09/16/10 21:17:32  nsrd re-setting overall number of authorized 
save sessions, changing value from (1) to (0)
    11348 09/16/10 21:17:41  nsrd deactivating mmd #1
    67898 09/16/10 21:17:41  nsrd Calling mm_deactivate for mmd 1 that is 
using device /dbu/dev.001 with volume XXX.001 on host XXX
    11348 09/16/10 21:17:41  nsrd deactivating mmd #2

...etc.

After I killed the savegrp process, stopped and restarted Networker, it 
again has worked normally more than once. There was nothing apparently 
wrong or strange in regard to the system in general, nor specifically to 
Networker before this happened AFAICT. The last time was months ago, but 
it was the same idential behavior. It's not limited to just a subset of 
the AFTDs, either. Entries referencing all 11 of them can be found during 
the time this was happening. 

Any ideas? Known bug?  :-)

Thanks!

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