Dear Marian,
Thanks for answers.
but after deep investigation i found sniffed messages presented below.
As i understand chan.rtp is releasing the rtp legs while receiving reinvite and after changing localport param.
Please can you advise how can we fix this issue 

Sniffed 'chan.rtp' time=1455181133.881092
  thread=0x1940a20 'YSIP EndPoint'
  data=(nil)
  retval='(null)'
  param['rtpid'] = 'yrtp/1362960942'
  param['media'] = 'audio'
  param['transport'] = 'RTP/AVP'
  param['terminate'] = 'true'
  param['call_direction'] = 'incoming'
  param['call_address'] = 'y.y.y.y:5060'
  param['call_status'] = 'answered'
  param['call_billid'] = '1454933764-119801'
Returned true 'chan.rtp' delay=0.000047
  thread=0x1940a20 'YSIP EndPoint'
  data=(nil)
  retval='(null)'
  param['rtpid'] = 'yrtp/1362960942'
  param['media'] = 'audio'
  param['transport'] = 'RTP/AVP'
  param['terminate'] = 'true'
  param['call_direction'] = 'incoming'
  param['call_address'] = 'y.y.y.y:5060'
  param['call_status'] = 'answered'
  param['call_billid'] = '1454933764-119801'
  param['handlers'] = 'yrtp:100'
  param['localip'] = 'x.x.x.x'
  param['localport'] = '25318'
  param['stats'] = 'PS=45538,OS=910760,PR=45000,OR=900000,PL=0'
  param['status'] = 'terminated'
20160211085853.881178 >>> DataTranslator::detachChain(0x7fbee40b14a0,0x7fbcfc0d26a0)
20160211085853.881189 <<< DataTranslator::detachChain
20160211085853.881198 >>> DataTranslator::detachChain(0x7fbcfc150080,0x7fbee409f0d0)
20160211085853.881204 <<< DataTranslator::detachChain
20160211085853.881216 <ALL> Cleaning up RTP 0x7fbee40ac480 [0x7fbee4044970]
Sniffed 'chan.rtp' time=1455181133.881291
  thread=0x1940a20 'YSIP EndPoint'
  data=0x7fbedc1155f0
  retval='(null)'
  param['id'] = 'sip/241959'
  param['module'] = 'sip'
  param['call_direction'] = 'incoming'
  param['call_address'] = 'y.y.y.y:5060'
  param['call_status'] = 'answered'
  param['call_billid'] = '1454933764-119801'
  param['media'] = 'audio'
  param['transport'] = 'RTP/AVP'
  param['direction'] = 'bidir'
  param['format'] = 'g729'
  param['ipv6_support'] = 'false'
  param['remoteip'] = 'y.y.y.y'
  param['remoteport'] = '9746'
  param['evpayload'] = '96'
  param['sdp_maxptime'] = '20'
  param['sdp_3gOoBTC'] = ''
20160211085853.881409 <INFO> DataTranslator::attachChain [0x7fbedc109700] '(null)' -> [0x7fbcfc0d26a0] 'g729' not possible
20160211085853.881428 <INFO> DataTranslator::attachChain [0x7fbcfc150080] 'g729' -> [0x7fbedc081fc0] '(null)' not possible
20160211085853.881456 >>> DataTranslator::detachChain(0x7fbedc109700,0x7fbcfc0d26a0)
20160211085853.881466 <<< DataTranslator::detachChain
20160211085853.881476 <ALL> DataTranslator::attachChain [0x7fbedc109700] 'g729' -> [0x7fbcfc0d26a0] 'g729' succeeded
20160211085853.881482 >>> DataTranslator::detachChain(0x7fbcfc150080,0x7fbedc081fc0)
20160211085853.881486 <<< DataTranslator::detachChain
20160211085853.881492 <ALL> DataTranslator::attachChain [0x7fbcfc150080] 'g729' -> [0x7fbedc081fc0] 'g729' succeeded
Returned true 'chan.rtp' delay=0.000257
  thread=0x1940a20 'YSIP EndPoint'
  data=0x7fbedc1155f0
  retval='(null)'
  param['id'] = 'sip/241959'
  param['module'] = 'sip'
  param['call_direction'] = 'incoming'
  param['call_address'] = 'y.y.y.y:5060'
  param['call_status'] = 'answered'
  param['call_billid'] = '1454933764-119801'
  param['media'] = 'audio'
  param['transport'] = 'RTP/AVP'
  param['direction'] = 'bidir'
  param['format'] = 'g729'
  param['ipv6_support'] = 'false'
  param['remoteip'] = 'y.y.y.y'
  param['remoteport'] = '9746'
  param['evpayload'] = '96'
  param['sdp_maxptime'] = '20'
  param['sdp_3gOoBTC'] = ''
  param['handlers'] = 'yrtp:100'
  param['localip'] = 'x.x.x.x'
  param['localport'] = '16950'
  param['rtpid'] = 'yrtp/70563133'
  param['status'] = 'created'