Merging on all field names may be slightly too aggressive, as matches on fields with the same name may not necessarily mean they are suitable to be used in a join criteria. Instead we may implement functionality where if you add another join criteria it will automatically choose the first field where the names are the same that hasn't yet been selected. I'm unsure when this will be implemented, but it may be towards the tail end of 2.6 development or in 2.7.