So guess what I just ran into the exact same thing with the nice "side-effect" that my changes I do in online mode aren't picked up by the OBIPS whereas the OBIS holds it. Will create an own thread for that
As to your question: Look for "metadataUpdateDefault_diff.xml" and not "default_diff.xml".
Is the "metadataUpdateDefault_diff.xml" located in the same directory as the liverpd.rpd? I don't recall seeing it there...
One deeper. /ssi/metadata/datamodel/metadataUpdate