It seems that even though after detecting polarity reversal on asterisk, Asterisk does not answer the call.
On further debugging on the issue it seems that, if “answeronpolarityswitch” is set to “yes” and “callprogress” is set to “no” as soon as call is answered and polarity reversal is detected by asterisk, Asterisk change the call state to UP but actually doesnot sending CONTORL_ANSWER frame to core.