Index: wp-includes/js/media-views.js
===================================================================
--- wp-includes/js/media-views.js	(revision 23005)
+++ wp-includes/js/media-views.js	(working copy)
@@ -3553,7 +3553,7 @@
 		update: function( key ) {
 			var value = this.model.get( key ),
 				$setting = this.$('[data-setting="' + key + '"]'),
-				$buttons;
+				$buttons, $value;
 
 			// Bail if we didn't find a matching setting.
 			if ( ! $setting.length )
@@ -3564,8 +3564,16 @@
 
 			// Handle dropdowns.
 			if ( $setting.is('select') ) {
-				$setting.find('[value="' + value + '"]').attr( 'selected', true );
+				$value = $setting.find('[value="' + value + '"]');
 
+				if ( $value.length ) {
+					$value.attr( 'selected', true );
+				} else {
+					// If we can't find the desired value, record what *is* selected.
+					this.model.set( $setting.data('setting'), $setting.find('[selected]').val() );
+				}
+
+
 			// Handle button groups.
 			} else if ( $setting.hasClass('button-group') ) {
 				$buttons = $setting.find('button').removeClass('active');
Index: wp-includes/media.php
===================================================================
--- wp-includes/media.php	(revision 23005)
+++ wp-includes/media.php	(working copy)
@@ -1832,10 +1832,10 @@
 						<#
 						var size = data.sizes['<?php echo esc_js( $value ); ?>'];
 						if ( size ) { #>
-							<option value="<?php echo esc_attr( $value ); ?>" <?php selected( $value, 'medium' ); ?>>
+							<option value="<?php echo esc_attr( $value ); ?>" <?php selected( $value, 'full' ); ?>>
 								<?php echo esc_html( $name ); ?> &ndash; {{ size.width }} &times; {{ size.height }}
 							</option>
-						<# } #>>
+						<# } #>
 					<?php endforeach; ?>
 				</select>
 			</label>