losing data during cp -a

I'm faced with a dispute regarding the loss of directories during a 
software upgrade (specifically, upgrading a Drupal installation).

I'm responsible for security upgrades, and the other dude does development.

as part of the security upgrade process, I did:

# cp -a sites ~/backup-sites-folder

..... unpack new drupal core, including the default sites directory .....

# rm -r sites
# cp -a ~/backup-sites-folder sites

Somewhere a sub-directory of "sites" disappeared causing the system to fail.

So the question is: how often would a sub-directory simply disappear 
during a cp process without an error message? Personally I've never seen 
it happen. I wonder if someone else has?

-- 
David McQuire
0418 310312

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