diff --git a/wp-includes/js/media-models.js b/wp-includes/js/media-models.js
index 2e924ac89d..20095dbf60 100644
--- a/wp-includes/js/media-models.js
+++ b/wp-includes/js/media-models.js
@@ -697,4 +697,77 @@ window.wp = window.wp || {};
 		}
 	});
 
+	/**
+	 * wp.media.model.Composite
+	 *
+	 * Creates a model that can simultaneously pull from two or more collections.
+	 */
+	media.model.Composite = Attachments.extend({
+		initialize: function( models, options ) {
+			this.observe( this, { silent: true });
+			Attachments.prototype.initialize.apply( this, arguments );
+		},
+
+		evaluate: function( attachment, options ) {
+			var valid = this.validator( attachment ),
+				hasAttachment = !! this.getByCid( attachment.cid );
+
+			if ( ! valid && hasAttachment ) {
+				this.remove( attachment, options );
+			} else if ( valid && ! hasAttachment ) {
+				this.add( attachment, options );
+
+				// If we haven't been silenced, resort the collection.
+				if ( this.comparator && ( ! options || ! options.silent ) )
+					this.sort({ silent: true });
+			}
+
+			return this;
+		},
+
+		validator: function() {
+			return true;
+		},
+
+		evaluateAll: function( attachments, options ) {
+			_.each( attachments.models, function( attachment ) {
+				this.evaluate( attachment, { silent: true });
+			}, this );
+
+			if ( this.comparator )
+				this.sort( options );
+			return this;
+		},
+
+		observe: function( attachments, options ) {
+			var silent = options && options.silent;
+
+			attachments.on( 'add remove',  silent ? this._evaluateSilentHandler : this._evaluateHandler, this );
+			attachments.on( 'reset',  silent ? this._evaluateAllSilentHandler : this._evaluateAllHandler, this );
+
+			this.evaluateAll( attachments, options );
+		},
+
+		unobserve: function( attachments ) {
+			attachments.off( 'add remove', this._evaluateHandler, this );
+			attachments.off( 'reset', this._evaluateAllHandler, this );
+		},
+
+		_evaluateHandler: function( attachment, attachments, options ) {
+			return this.evaluate( attachment, options );
+		},
+
+		_evaluateAllHandler: function( attachments, options ) {
+			return this.evaluateAll( attachments, options );
+		},
+
+		_evaluateSilentHandler: function( attachment, attachments, options ) {
+			return this.evaluate( attachment, _.defaults({ silent: true }, options ) );
+		},
+
+		_evaluateAllSilentHandler: function( attachments, options ) {
+			return this.evaluateAll( attachments, _.defaults({ silent: true }, options ) );
+		}
+	});
+
 }(jQuery));
\ No newline at end of file
diff --git a/wp-includes/js/media-views.js b/wp-includes/js/media-views.js
index 0ff3493d58..17e782e398 100644
--- a/wp-includes/js/media-views.js
+++ b/wp-includes/js/media-views.js
@@ -681,52 +681,32 @@
 			_.each(['gallery-library','gallery-upload'], function( id ) {
 				var state = this.get( id ),
 					original = state.get('_library'),
-					skeleton;
+					composite;
 
 				// Remember the state's original library.
 				if ( ! original )
 					state.set( '_library', original = state.get('library') );
 
-				// Create a skeleton library in its place.
-				skeleton = new Attachments( null, {
+				// Create a composite library in its place.
+				composite = new media.model.Composite( null, {
 					props: _.pick( original.props.toJSON(), 'order', 'orderby' )
 				});
 
-				// Rejects attachments that do not exist in the original library
-				// or that do exist edit state's library.
-				skeleton.filters.difference = function( attachment ) {
-					return ! original.getByCid( attachment.cid ) || !! editLibrary.getByCid( attachment.cid );
+				// Accepts attachments that exist in the original library and
+				// that do not exist in the state's library.
+				composite.validator = function( attachment ) {
+					return !! original.getByCid( attachment.cid ) && ! editLibrary.getByCid( attachment.cid );
 				};
 
-				skeleton.evaluate = function( attachment ) {
-					var valid = ! this.validator( attachment ),
-						inSkeleton = !! this.getByCid( attachment.cid );
+				composite.observe( original );
+				composite.observe( editLibrary );
 
-					if ( ! valid && inSkeleton )
-						this.remove( attachment );
-					else if ( valid && ! inSkeleton )
-						this.add( attachment ).sort();
+				// When `more()` is triggered on the composite collection,
+				// pass the command over to the `original`, which will
+				// populate the query.
+				composite.more = _.bind( original.more, original );
 
-					return this;
-				};
-
-				skeleton.evaluateAll = function ( attachments ) {
-					_.each( attachments.models, this.evaluate, this );
-					return this;
-				};
-
-				skeleton.on( 'add remove', skeleton.evaluate, skeleton );
-				skeleton.on( 'reset', skeleton.evaluateAll, skeleton );
-				editLibrary.on( 'add remove', skeleton.evaluate, skeleton );
-				editLibrary.on( 'reset', skeleton.evaluateAll, skeleton );
-
-				// Mirror the original library.
-				skeleton.mirror( original );
-
-				// Ensure we've evaluated everything in the edit library.
-				skeleton.evaluateAll( editLibrary );
-
-				state.set( 'library', skeleton );
+				state.set( 'library', composite );
 			}, this );
 		},