What is the REAL Address of this List

In recent weeks I've received quite a few posts where the original
included both:
   http-wg@cuckoo.hpl.hp.com and
   http-wg@hplb.hpl.hp.com

Replying without deleting the second address results in a bounce message
for unknown user.  Where is this stray address coming from and can we
try and stop including it?

The evidence would seem to be that the convoluted ?UUCP? gateway address
which seems to be in my address book from historical times works but isn't
necessary?

Dave Morris