Ring group quandry

I have three extensions in a ring group (600), 101, 103 and 106. When an incoming call comes in it rings as expected to both extensions, however when one extension picks up, the other keeps ringing, even after the call is terminated. The only way to stop the ringing is if the offending phone physically picks up and then hangs up.

Asterisk (Ver. 1.8.28.2)
FreePBX 2.11.0.38

Please let me know what other info you may need to help me on this.
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Thanks in advance!!

It would be helpful to know what brand and model of phone. Would these be analog phones? It would also be helpful to have a call trace.

The phones are Grandstream GXP2000, and the trace can be seen at http://pastebin.com/8u10j7Li

Summary, a call was placed from ######1925 to ######4255. Extension 103 picked up the call, but extensions 101 and 106 kept ringing even after the call was answered and terminated. They continued to ring until the handsets were re seated.

Thank you!!

[SOLVED] sort of, let me explain…

I was trying to accomplish this on a cloud server using Amazon’s AWS server, and this was the only piece that I could not make work. When I moved the config to a local server, all worked as expected.