Index: wp-admin/js/customize-controls.js
===================================================================
--- wp-admin/js/customize-controls.js	(revision 28734)
+++ wp-admin/js/customize-controls.js	(working copy)
@@ -991,11 +991,14 @@
 
 				if ( 0 === processing() ) {
 					submit();
+					$('.upload-dropzone .spinner').remove();
 				} else {
+					$('.upload-dropzone').append('<div class="spinner" style="display:block"><\/div>');
 					submitWhenDoneProcessing = function () {
 						if ( 0 === processing() ) {
 							api.state.unbind( 'change', submitWhenDoneProcessing );
 							submit();
+							$('.upload-dropzone .spinner').remove();
 						}
 					};
 					api.state.bind( 'change', submitWhenDoneProcessing );