I too am having this problem. Are the reinvites being generated by Asterisk? I have a test environment where making adding two lines of code to asterisk will help the issue. My only concern is whether the code change creates a performance issue. I tried asking the question the asterisk-dev list, but did not get a response. My solution was to insert a usleep(20000) between the ack and the reinvite. This delays the reinvite by 20 ms.

The concern I had was is Asterisk fully threaded or does the 20 ms delay delay all processing of sip requests.

Gene