patch 7.4.1961
Problem:    When 'insertmode' is reset while doing completion the popup menu
            remains even though Vim is in Normal mode.
Solution:   Ignore stop_insert_mode when the popup menu is visible.  Don't set
            stop_insert_mode when 'insertmode' was already off. (Christian
            Brabandt)
diff --git a/src/option.c b/src/option.c
index b17fc28..80bd867 100644
--- a/src/option.c
+++ b/src/option.c
@@ -8001,7 +8001,8 @@
 		need_start_insertmode = TRUE;
 	    stop_insert_mode = FALSE;
 	}
-	else
+	/* only reset if it was set previously */
+	else if (old_value)
 	{
 	    need_start_insertmode = FALSE;
 	    stop_insert_mode = TRUE;