Calls between extensions within office also ring at reception

We had our new phone system at our office installed 2 weeks ago and, since the beginning, every time someone within our office calls someone on another extension within our office, that call will also ring at the receptionist's desk every time. It's almost like interoffice calls are being labeled as incoming calls somehow. But it's rightfully driving our receptionist crazy as now she hears double the ringing all day long. We've updated all the firmware, unplugged and restarted all the phones as Comcast always says to do in any situation, but it hasn't done anything. Nearly all of the extensions at the office are not set to auto-forward any calls or forward to cell phones or anything either. So we aren't sure what the problem is. The customer service person who came last week said that was "really weird" and said she would have to "take this back to the company" then hasn't responded to us for another week. We really need this taken care of ASAP.

We all have the Polycom VVX 411 HD (including the receptionist who also has a "sidekick" console extension added on to hers except for one colleague who has the Polycom VVX 501 HD because Comcast ran out of the older one. Would greatly appreciate any help.