Jonathan recommended:

> > use the supplied default nsswitch.conf
> > 
> > 	passwd:  compat
> > 
> > line, but instead use
> > 
> > 	passswd: nis [notfound=return] files

This has resolved my issue without any adverse affects.  I'm not exactly
clear on what the trade off is on either configuration.  As noted by 
others, there definitely is a bug with the default option which surfaces
with larger installations running 3.x.  For now, I'm fine with the second 
config option, which seems to work as expected.