I have a theory, but bare with me because it's just a massive guess.
I have noticed a pattern:

*There's a bigger than usual quake between el hierro and (I think) Tenerife.. (last one was a 3.something) and then activity picks up under el hierro.

*Then seismos from la palma and the other islands start to show little tremors and/or deformation.

*Then activity on el Hierro drops.

*Then there's another quake/tremor, and the process begins again.

I theorise that el hierro is (as we've affectionately started calling it..) a ''windbag''
Magma travels from the area where the bigger quakes/tremors occur, then it takes a route directly around/under el hierro, activity picks up, and it swells i.e. deformity happens, then it moves off and continues it's journey towards la palma..

I think BOB was a fluke, some pressure was released, but it wasn't meant to erupt there...
I think La palma or one of the other islands is being 'fed' and the route the magma takes is around or under el hierro.

The only way I can think to prove it, is to watch this recent flurry of activity, then watch la palma closely in the weeks that follow.
If this is the case then something will have to give, either it'll find a route out on el hierro, or it'll take a long while yet for la palma to be fed to the point that it's ready to burst.

Like I say... just a theory.. thoughts?
:)