I don´t know if this is you case. I ask if you always connect to the same port or a diferent port?
That behavior is normal for some printers and/or printer drivers if you chage the usb cabe to another port, on the computer or the port replicator. For test purpuses make sure that you alway connect to the exact same ports and check if it still hapens. When you have normal and well designed usb printers no matter to what port you connect them the computer still sees it as the same printer (for example by it's serial number) and there for doesn't add a new one. For other printers that doesn't happen so the computer/driver identifies the printer by the id of the port. That is normal. That happens for example to allow you to connect two or more printers like yours to the same computer. They are distinguished by the port that they are connected. Another thing when using using usb to serial adapters they are assigned a com port (COM 4, COM 5, ...) depending on the usb port that you connect them, thus allowing you to connect several usb to serial adapters and make available serel COM ports ports without interfering in the others.
Hope this helps
Regards
Joel