patch 7.4.882
Problem:    When leaving the command line window with CTRL-C while a
            completion menu is displayed the menu isn't removed.
Solution:   Force a screen update. (Hirohito Higashi)
diff --git a/src/edit.c b/src/edit.c
index db4a079..bd5c57e 100644
--- a/src/edit.c
+++ b/src/edit.c
@@ -3903,6 +3903,12 @@
 		showmode();
 	    }
 
+#ifdef FEAT_CMDWIN
+	    if (c == Ctrl_C && cmdwin_type != 0)
+		/* Avoid the popup menu remains displayed when leaving the
+		 * command line window. */
+		update_screen(0);
+#endif
 #ifdef FEAT_CINDENT
 	    /*
 	     * Indent now if a key was typed that is in 'cinkeys'.