Models in Ember extend the DS.Model prototype. This means that arrays and object literals defined as properties will be shared amongst instances of that model. If you want to define a property in a mixin that is not shared, you can define it either as a computed property or have it be created on initialization of the object.

export default DS.Model.extend({
  // filters array will be shared amongst all instances of the model.
  filters: Ember.A(),

  // filters will be a separate array for every instance of the model
  filters: Ember.computed(function() {
    return Ember.A();
  })
});