Strange issue when being put on hold

Hi all,

I have a very strange issue. When put on hold by some called parties (does not affect all called parties, but can be reproduced with certain called PBXs) out local FreePBX play music on hold and the called party can still here us talking! I tried to trace this, but I do not see anything special coming from the SIP-Trunk.

x.x.x.x is the IP of the SIP-provider
y.y.y.y is the local IP-address

    == Using SIP RTP TOS bits 184
  == Using SIP RTP CoS mark 5
    -- Called SIP/Toplink/07150300628
    -- SIP/Toplink-0000149f is making progress passing it to SIP/00-0000149e
    -- SIP/Toplink-0000149f is making progress passing it to SIP/00-0000149e
       > 0xb752ac00 -- Probation passed - setting RTP source address to x.x.x.x:11886
    -- SIP/Toplink-0000149f is making progress passing it to SIP/00-0000149e
       > 0xb752ac00 -- Probation passed - setting RTP source address to x.x.x.x:11886
    -- SIP/Toplink-0000149f is ringing
    -- SIP/Toplink-0000149f is making progress passing it to SIP/00-0000149e
       > 0xb752ac00 -- Probation passed - setting RTP source address to x.x.x.x:11886
    -- SIP/Toplink-0000149f answered SIP/00-0000149e
       > 0xb752ac00 -- Probation passed - setting RTP source address to x.x.x.x:11886
       > 0xb732ab80 -- Probation passed - setting RTP source address to y.y.y.y:2260
  == Using UDPTL TOS bits 184
  == Using UDPTL CoS mark 5
  == Using UDPTL TOS bits 184
  == Using UDPTL CoS mark 5
    -- Started music on hold, class 'default', on SIP/00-0000149e
       > 0xb752ac00 -- Probation passed - setting RTP source address to x.x.x.x:11886
       > 0xb752ac00 -- Probation passed - setting RTP source address to x.x.x.x:11886
       > 0xb732ab80 -- Probation passed - setting RTP source address to y.y.y.y:2260



  == Using SIP RTP TOS bits 184
  == Using SIP RTP CoS mark 5
    -- Called SIP/Toplink/07150300628
    -- SIP/Toplink-0000149f is making progress passing it to SIP/00-0000149e
    -- SIP/Toplink-0000149f is making progress passing it to SIP/00-0000149e
       > 0xb752ac00 -- Probation passed - setting RTP source address to x.x.x.x:11886
    -- SIP/Toplink-0000149f is making progress passing it to SIP/00-0000149e
       > 0xb752ac00 -- Probation passed - setting RTP source address to x.x.x.x:11886
    -- SIP/Toplink-0000149f is ringing
    -- SIP/Toplink-0000149f is making progress passing it to SIP/00-0000149e
       > 0xb752ac00 -- Probation passed - setting RTP source address to x.x.x.x:11886
    -- SIP/Toplink-0000149f answered SIP/00-0000149e
       > 0xb752ac00 -- Probation passed - setting RTP source address to x.x.x.x:11886
       > 0xb732ab80 -- Probation passed - setting RTP source address to y.y.y.y:2260
  == Using UDPTL TOS bits 184
  == Using UDPTL CoS mark 5
  == Using UDPTL TOS bits 184
  == Using UDPTL CoS mark 5
    -- Started music on hold, class 'default', on SIP/00-0000149e
       > 0xb752ac00 -- Probation passed - setting RTP source address to x.x.x.x:11886
       > 0xb752ac00 -- Probation passed - setting RTP source address to x.x.x.x:11886
       > 0xb732ab80 -- Probation passed - setting RTP source address to y.y.y.y:2260

Has anybody an idea why this happens?

Kind regards,
Jens