Yes. I just noticed something also. The url looks strange to me. There are two "rectype=" in the query string. The first one is the custom record, the second is the child. I wonder if it's confusing them and telling me the form isn't the one for the child record...

rectype=373&id=1510&scrollid=96762&rectype=374&whence=&e=T&selectedtab=custom52