Index: wp-admin/js/common.js
===================================================================
--- wp-admin/js/common.js	(revision 22572)
+++ wp-admin/js/common.js	(working copy)
@@ -397,7 +397,7 @@
 		button = form.find('input[type="submit"]');
 		input = form.find('input[type="file"]');
 		function toggleUploadButton() {
-			button.prop('disabled', '' === input.val());
+			button.prop('disabled', '' === input.filter(':visible').val());
 		}
 		toggleUploadButton();
 		input.on('change', toggleUploadButton);
Index: wp-admin/media-upload.php
===================================================================
--- wp-admin/media-upload.php	(revision 22572)
+++ wp-admin/media-upload.php	(working copy)
@@ -87,7 +87,7 @@
 
 	require_once('./admin-header.php');
 
-	$form_class = 'media-upload-form type-form validate';
+	$form_class = 'media-upload-form wp-upload-form type-form validate';
 
 	if ( get_user_setting('uploader') )
 		$form_class .= ' html-uploader';