Index: src/js/_enqueues/vendor/tinymce/plugins/wordpress/plugin.js
===================================================================
--- src/js/_enqueues/vendor/tinymce/plugins/wordpress/plugin.js	(revision 43331)
+++ src/js/_enqueues/vendor/tinymce/plugins/wordpress/plugin.js	(working copy)
@@ -113,8 +113,12 @@
 						'alt="" title="' + title + '" data-mce-resize="false" data-mce-placeholder="1" />' );
 			}
 
-			if ( event.load && event.format !== 'raw' && hasWpautop ) {
-				event.content = wp.editor.autop( event.content );
+			if ( event.load && event.format !== 'raw' ) {
+				if ( hasWpautop ) {
+					event.content = wp.editor.autop( event.content );
+				} else {
+					event.content = event.content.replace( /-->\s+<!--/g, '--><!--' );
+				}
 			}
 
 			if ( event.content.indexOf( '<script' ) !== -1 || event.content.indexOf( '<style' ) !== -1 ) {
@@ -608,6 +612,8 @@
 
 		if ( hasWpautop ) {
 			event.content = wp.editor.removep( event.content );
+		} else {
+			event.content = event.content.replace( /-->\s*<!-- wp:/g, '-->\n\n<!-- wp:' );
 		}
 	});