A patch for bootstrap-select v1.5.4 to fix the setStyle function. Currently setStyle doesn't properly keep track of what style was set previously, so the old style is never removed.

bootstrap-select-setStylePatch.js

(function(){

  //create a select so we can access the selectpicker
  var $div = $("<div><select></select></div>");

  //get the prototype
  var prototype = $div.find("select").selectpicker().data("selectpicker").constructor.prototype;

  //keep track of the original setStyle
  var setStyle = prototype.setStyle;

  prototype.setStyle = function(style, status) {
    //call original setStyle
    setStyle.apply(this, arguments);

    //THE ONLY CHANGE - SAVE STYLE SO IT CAN BE REMOVED NEXT TIME
    if (style) {
      this.options.style = style;
    }
  };

  //get rid of our temporary div
  $div.remove();

})();