The forecasting follies with respect to the MJO are a microcosm of why so many forecasts mishandle ENSO....if you think about it, this makes sense because why is ENSO even important? It is ONE OF the main determinants that dictate the origin, placement and ultimate evolution of the MJO.
The fact of the matter is that like ENSO events, not all MJO events are created equally, and it is a knowledge of the interaction with other ambient atmospheric variables that informs our knowledge of this....IE Just as one weak la nina event may be east based, and impacts the MJO quite differently then a west based (modoki event), it may also be more or less coupled with the atmosphere. This is also applicable to MJO waves in that you need to also study the ambient hemispheric landscape in order to determine how coherent the MJO wave will be, which is to say what other factors will attenuate or augment its impact on the pattern.