fun1 f = fun2
  where
    fun2 :: .c
    fun2
      | g f = undef
    g :: (.b -> .b) -> Bool
    g _ = True

was
  [o u[11651944]:a -> u[11651944]:a]  -> c[11210672]:c
but st_attr_vars was
  [c[11210672], c[11210672]]
(u[11651944] is missing)