Ticket #28815: 28815.1.diff

src/wp-admin/js/post.js

@@ -423 +423 @@
                         return;
                 }
 
-                if ( $button.hasClass('submitdelete') || $button.is( '#post-preview' ) ) {
+                if ( $button.hasClass( 'submitdelete' ) ){
+                        releaseLock = false;
+                        $(window).off( 'beforeunload.edit-post' );
+                        return;
+                }
+
+                if ( $button.is( '#post-preview' ) ) {
                         return;
                 }