Hello jgranade,
welcome back to the Polycom Community.
The community's VoIP FAQ contains this post here:
Oct 7, 2011 Question: Can I register or is my Polycom Phone compatible with a “XYZ” SIP Server?
Resolution: Please check => here<=
The above shows an easy simply illustration how to register one line and the relevant configuration if not done so via the Web Interface.
The exact same matches for additional lines and I can only assume you somehow got something mixed up.
Try to factory restore and follow the above.
If we would have a bug in something so simple we would be inundated with tickets.
Please ensure to provide some feedback if this reply has helped you so other users can profit from your experience.
Best Regards
Steffen Baier
Polycom Global Services