Other phones continue to ring after incoming call answered

Anyone know why all my other phones continue to ring after I have already answered the incoming call? They will ring for about 30 seconds then stop. This happens randomly. Probably once every 20 calls. I can’t reproduce the error unless i try to make about 20 incomming calls. I am using asterisk ring groups and my phone company has a ring down pool of numbers it dials. Could those cause this? I am using Polycom 601 phones and Digium POTS Cards with 6 phone lines. The version of asterisk im running is:
Asterisk 1.2.4 built by root @ asterisk.vjmemorials.local on a i686 running Linux on 2006-08-25 00:04:04 UTC

It is also Asterisk@home.

Also, about the same interval when answering incoming calls, the caller can’t hear the callee. These two issues seem independent of each other but are very anoying

Any thoughts or ideas on how I can go about trouble shooting these problems would be great!

You are running a version that is too old to realistically support, other than by replacing it with a current one.