src/Pure/Isar/isar_thy.ML

       let
         val sg = Theory.sign_of thy;
         val names = map (intern sg kind) xnames;
         val bads = filter_out (check sg) names;
       in
-        if null bads then Theory.hide_space_i (kind, names) thy
+        if null bads then Theory.hide_space_i true (kind, names) thy
         else error ("Attempt to hide undeclared item(s): " ^ commas_quote bads)
       end
   | None => error ("Bad name space specification: " ^ quote kind));
 
 in