Index: /trunk/ccl/hemlock/src/htext1.lisp
===================================================================
--- /trunk/ccl/hemlock/src/htext1.lisp	(revision 738)
+++ /trunk/ccl/hemlock/src/htext1.lisp	(revision 739)
@@ -181,5 +181,7 @@
   (when (bufferp buffer)
     (let* ((document (buffer-document buffer)))
-      (when document (document-begin-editing document)))))
+      (when document
+        (lock-buffer buffer)
+        (document-begin-editing document)))))
 
 (defun buffer-document-end-editing (buffer)
@@ -187,4 +189,5 @@
     (let* ((document (buffer-document buffer)))
       (when document
+        (unlock-buffer buffer)
         (document-end-editing document)))))