Index: src/wp-includes/js/media-views.js
===================================================================
--- src/wp-includes/js/media-views.js	(revision 29546)
+++ src/wp-includes/js/media-views.js	(working copy)
@@ -5009,6 +5009,13 @@
 				return;
 			}
 
+			// Bail if the model is already selected
+			if ( this.$el.hasClass( 'selected' ) ) {
+				return;
+			}
+
+			// Add 'selected' class to model. Set aria-checked to true.
+			// Make the checkbox tabable
 			this.$el.addClass( 'selected' ).attr( 'aria-checked', true )
 					.find( '.check' ).attr( 'tabindex', '0' );