Crosstalk - VoIP

Hello,

I'm wondering if the collective hive mind here could help me out explaining this in a manor that anyone could understand . Customer has an issue that the far end (calling party) can hear MoH when they are put through to an agent. Not that they hear just MoH, they can also hear the agent talking so MoH and agent audio at the same time. Now this is a fairly large customer and for this sector they have no control how calls come in. It's centrally managed and there are IVR, prompts, etc before it reaches the part I manage. The important part is, when it reaches and exits the bit under my control it is SIP end to end. Even on the gateway (CUBE). I've explained that it's pretty much impossible for crosstalk of hearing another audio source at the same time is impossible unless there is a problem with DSP which aren't being invoked. I could understand if you heard music on hold and then the agent or visa versa but never both at the same time in IP. I understand hissing, crackling, etc could occur if the cables were faulty but never clear MoH and agent at the same time. Now I understand that this sort of cross talk can occur on electrical circuits but not digital. The users I am working with cannot confirm if at some point further in the call it breaks in or out on POTS. Now they won't go to the team that manages anything passed what we manage until we can provide it's definetly not our equipment. I don't know how I can explain myself better, they are requesting somewhere in a SIP RFC why this cannot occur but it's more of why it occurs in electrical and not digital. Could someone maybe link me and explanation to why this kind of crosstalk doesn't occur in digital. All I can think of this point is pumping all calls to a recorder from the CUBE but theyll likely not pay for that and thus I'll be going around in circles and I'm clearly not getting my point across properly to the customer. Sorry if this seems like a silly question and thank you.