AS A verbal form, it is an uncommon localism of the area of Cuenca and Albacete (where this sense of the word has been collected) in the sense of making a fuss about people, assembling bulla (it could be the original etym) with concern before an event that is desired to occur. It also seems a local corruption of the verb rebullir: bulla comes from bullir and the analogy would not be uncommon. On the other hand, in some areas of the ancient Kingdom of León it is an allophonic deformation in the evolution of the collective noun rebollar, oak.
