Index: src/wp-admin/js/customize-controls.js
===================================================================
--- src/wp-admin/js/customize-controls.js	(revision 30984)
+++ src/wp-admin/js/customize-controls.js	(working copy)
@@ -128,12 +128,12 @@
 	api.utils.areElementListsEqual = function ( listA, listB ) {
 		var equal = (
 			listA.length === listB.length && // if lists are different lengths, then naturally they are not equal
-			-1 === _.map( // are there any false values in the list returned by map?
+			-1 === _.indexOf( _.map( // are there any false values in the list returned by map?
 				_.zip( listA, listB ), // pair up each element between the two lists
 				function ( pair ) {
 					return $( pair[0] ).is( pair[1] ); // compare to see if each pair are equal
 				}
-			).indexOf( false ) // check for presence of false in map's return value
+			), false ) // check for presence of false in map's return value
 		);
 		return equal;
 	};
Index: src/wp-includes/class-wp-customize-control.php
===================================================================
--- src/wp-includes/class-wp-customize-control.php	(revision 30984)
+++ src/wp-includes/class-wp-customize-control.php	(working copy)
@@ -738,7 +738,7 @@
 	 */
 	public function content_template() {
 		?>
-		<label for="{{ data.settings.default }}-button">
+		<label for="{{ data.settings['default'] }}-button">
 			<# if ( data.label ) { #>
 				<span class="customize-control-title">{{ data.label }}</span>
 			<# } #>
@@ -775,7 +775,7 @@
 			</div>
 			<div class="actions">
 				<button type="button" class="button remove-button"><?php echo $this->button_labels['remove']; ?></button>
-				<button type="button" class="button upload-button" id="{{ data.settings.default }}-button"><?php echo $this->button_labels['change']; ?></button>
+				<button type="button" class="button upload-button" id="{{ data.settings['default'] }}-button"><?php echo $this->button_labels['change']; ?></button>
 				<div style="clear:both"></div>
 			</div>
 		<# } else { #>
@@ -794,7 +794,7 @@
 				<# if ( data.defaultAttachment ) { #>
 					<button type="button" class="button default-button"><?php echo $this->button_labels['default']; ?></button>
 				<# } #>
-				<button type="button" class="button upload-button" id="{{ data.settings.default }}-button"><?php echo $this->button_labels['select']; ?></button>
+				<button type="button" class="button upload-button" id="{{ data.settings['default'] }}-button"><?php echo $this->button_labels['select']; ?></button>
 				<div style="clear:both"></div>
 			</div>
 		<# } #>