It seems there is a bug with vgimport if you import the volume group with the
'vgnamePV_EXP' name instead of just the original 'vgname' name.  I was able to
replicate this bug like so:

Create a volume group called, say, vgname.  Then ...
vgchange -an vgname
vgexport vgname
vgscan
- displays vgnamePV_EXP
vgimport vgnamePV_EXP <physical_volume>   <---- this is where the bug is
vgscan
- displays vgnamePV_EXP instead of vgname
pvscan
- still reports that the PVs are 'in EXPORTED VG "vgname"'

However if I use:
vgimport vgname <physical_volume>
vgscan
- displays vgname
pvscan
- shows normal/expected vgname information

Solution to the mess created:
vgrename vgnamePV_EXP vgname
... vgscan and pvscan show consistent information again.

Lesson learnt:
There is a bug in RHEL3 lvm if you use 'vgimport vgnamePV_EXP <physical_volume>'
instead of 'vgimport vgname <physical_volume>'