“Unexpected operator with clocked I/O” issue.

[fdtsaid]

In 2.2.6 Combining Reset and Clocks of Scade Language Primer, there is a code snippet as following:

node nat() returns (s: int32)

let

  s = 1 -> (1 + pre s);

tel

node rst_clk (clock rst:bool; clock h:bool) returns (s:int32; t: int32 when h)

let

  s = (restart nat every rst)();

  t = (restart nat every rst)(() when h);

tel

But kcg complains that

-- Unexpected operator with clocked I/O

-- The output variable t cannot be clocked because operator rst_clk/ is not expanded

How to understand the problem?