Problems mapping 2 messages into 1

Hi.

I'm facing a problem mapping 2 messages into 1.

I have a BPM that has 2 abstract messages. In a transformation step, i transform this two messages into one but when i check the IDOC that finally has arrived to R3 backend, the fields that belogns to one of the source messages doesn't appear.

In message mapping i select the two source messages and the target message and the same in interface mapping.

Because is a transformation step inside the BPM, i can't see in SXI_MONITOR what's happening.

any idea of what's happening?

Regards.

Inigo.