diff --git a/libbalsa/imap/imap-handle.c b/libbalsa/imap/imap-handle.c
index 4d62c27e1..536126e45 100644
--- a/libbalsa/imap/imap-handle.c
+++ b/libbalsa/imap/imap-handle.c
@@ -548,6 +548,8 @@ imap_handle_idle_disable(ImapMboxHandle *h)
 gboolean
 imap_handle_op_cancelled(ImapMboxHandle *h)
 {
+  g_return_val_if_fail(h != NULL, FALSE);
+
   return h->op_cancelled;
 }
 
diff --git a/src/folder-conf.c b/src/folder-conf.c
index fe20d7458..845476b94 100644
--- a/src/folder-conf.c
+++ b/src/folder-conf.c
@@ -544,6 +544,8 @@ folder, parent);
             }
             if (button == GTK_RESPONSE_OK) {
                 GError* err = NULL;
+                const gchar *p, *q, *r;
+
                 /* Close the mailbox before renaming,
                  * otherwise the rescan will try to close it
                  * under its old name.
@@ -564,34 +566,44 @@ folder, parent);
                 sdd->mbnode->dir = g_strdup(parent);
 
                 /*  Rescan as little of the tree as possible. */
-                if (sdd->old_parent
-                    && !strncmp(parent, sdd->old_parent, strlen(parent))) {
-                    /* moved it up the tree */
-		    BalsaMailboxNode *mbnode =
-                        balsa_find_dir(sdd->parent->server, parent);
-                    if (mbnode) {
-                        balsa_mailbox_node_rescan(mbnode);
-			g_object_unref(mbnode);
-		    } else
-                        printf("Parent not found!?\n");
-                } else if (sdd->old_parent
-                           && !strncmp(parent, sdd->old_parent,
-                                       strlen(sdd->old_parent))) {
-                    /* moved it down the tree */
-		    BalsaMailboxNode *mbnode =
-			balsa_find_dir(sdd->parent->server, sdd->old_parent);
-                    if (mbnode) {
+                /* Find the longest common prefix of the new parent and
+                 * the old parent, and rescan there. */
+                p = parent;
+                q = sdd->old_parent;
+                r = NULL;
+
+                while (*p != '\0' && *q != '\0' && *p == *q) {
+                    if (*p == sdd->mbnode->delim)
+                        r = p;
+                    p++;
+                    q++;
+                }
+
+                if (*p == '\0' && *q == '\0') {
+                    /* No change of parent, just rename in place; we
+                     * could possibly modify the tree without going to
+                     * the server, but if we rescan the parent we can be
+                     * sure that we see it the same way as the server. */
+                    balsa_mailbox_node_rescan(sdd->mbnode->parent);
+                } else if (r == NULL) {
+                    /* No common ancestor, must rescan the whole tree */
+                    BalsaMailboxNode *mbnode = sdd->mbnode->parent;
+
+                    while ((mbnode->mailbox != NULL) && (mbnode->parent != NULL))
+                        mbnode = mbnode->parent;
+                    balsa_mailbox_node_rescan(mbnode);
+                } else {
+		    BalsaMailboxNode *mbnode;
+
+                    /* r points to the last delimiter in parent, in the
+                     * common part of the path; we replace it with '\0'
+                     * to truncate the string. */
+                    parent[r - parent] = '\0';
+		    mbnode = balsa_find_dir(sdd->parent->server, parent);
+                    if (mbnode != NULL) {
                         balsa_mailbox_node_rescan(mbnode);
 			g_object_unref(mbnode);
 		    }
-                } else {
-                    /* moved it sideways: a chain of folders might
-                     * go away, so we'd better rescan the complete IMAP server
-                     */
-                    BalsaMailboxNode *mb = sdd->mbnode->parent;
-                    while ((mb->mailbox != NULL) && (mb->parent != NULL))
-                        mb = mb->parent;
-                    balsa_mailbox_node_rescan(mb);
                 }
             }
         }
diff --git a/src/main-window.c b/src/main-window.c
index a1d72726f..0a4be4381 100644
--- a/src/main-window.c
+++ b/src/main-window.c
@@ -1853,20 +1853,12 @@ threading_change_state(GSimpleAction * action,
     BalsaWindow *window = BALSA_WINDOW(user_data);
     GtkWidget *index;
     gboolean thread_messages;
-    BalsaMailboxNode *mbnode;
-    LibBalsaMailbox *mailbox;
 
     thread_messages = g_variant_get_boolean(state);
 
     index = balsa_window_find_current_index(window);
-    balsa_index_set_thread_messages(BALSA_INDEX(index), thread_messages);
-
-    /* bw->current_index may have been destroyed and cleared during
-     * set-threading: */
-    index = balsa_window_find_current_index(window);
-    if (index && (mbnode = BALSA_INDEX(index)->mailbox_node)
-        && (mailbox = mbnode->mailbox))
-        bw_enable_expand_collapse(window, mailbox);
+    if (index != NULL)
+        balsa_index_set_thread_messages(BALSA_INDEX(index), thread_messages);
 
     g_simple_action_set_state(action, state);
 }