doc shows up on multiple printers

I would have thought this impossible, but:

First try:

2 XP clients on Win2k domain.

2 HP4200N printers connected via TCP/IP. On each of two
clients, one printer added, same printer names assigned on
each client, but different IP addresses specified.

Each client's printed output (to default printer) shows up
on BOTH printers.

Second try:

Same 2 Win XP clients and Win 2K domain; printers added
above deleted on both clients.

2 HP 4200N printers connected via ethernet, setup and
shared on server, one printer added discretely to each
client (so, each client has its "own" printer). On each
client, its respective 4200N printer is set as default.

Each client's printed output (to default printer) shows up
on BOTH printers.

Somebody tell me how this is possible.