Index: wp-includes/js/autosave.dev.js
===================================================================
--- wp-includes/js/autosave.dev.js	(revision 18515)
+++ wp-includes/js/autosave.dev.js	(working copy)
@@ -61,6 +61,17 @@
 	doPreview = function() {
 		$('input#wp-preview').val('dopreview');
 		$('form#post').attr('target', 'wp-preview').submit().attr('target', '');
+
+		/*
+		 * Workaround for WebKit bug preventing a form submitting twice to the same action.
+		 * https://bugs.webkit.org/show_bug.cgi?id=28633
+		 */
+		if ( $.browser.safari ) {
+			$('form#post').attr('action', function(index, value) {
+				return value + '?t=' + new Date().getTime();
+			});
+		}
+
 		$('input#wp-preview').val('');
 	}