Hearing IVR in the background when on a line

Hi !
I am running a FreePBX 2.3.1.5 and have noticed that the IVR starts running the welcome message when i am active on a SIP channel. (The problem sometimes acures severel minutes in the call). I have a sipura handeling 1 incoming PSTN line and a SIP Trunk for outgoing calls. Has anyone heard of this problem ?

Thanks