Error during test of a (package) function that returns a BOOLEAN (4334638)

If I debug a PL/SQL function (in a package) that returns a BOOLEAN then the automatically generated test script contains an extra string 'PL/SQL' that causes TOAD to finish the test with an error.

Here's a simple package specification that creates the error:
CREATE OR REPLACE PACKAGE  toadtest
IS
   FUNCTION store (p_msg IN VARCHAR2)
      RETURN BOOLEAN;
END toadtest;
/

Here's the package Body:
CREATE OR REPLACE PACKAGE BODY toadtest
IS
   FUNCTION store (p_msg IN VARCHAR2)
      RETURN BOOLEAN
      IS BEGIN
        RETURN TRUE;
      END;
END toadtest;
/

To test the function I right-click in the package body Editor window, choose 'Execute' and then 'Execute PL/SQL (debugger)'.

This opens the Parameter window. After entering the parameter values and pressing 'Execute' TOAD fails after a few seconds with an error message.

The cause is that TOAD adds the string 'PL/SQL'  to the definition of the return value .