Inheritance breaks if the parent has an external declaration

[sjoelund.se]

function myacos
  input Real x;
  output Real y;
external "builtin" y=acos(x);
end myacos;
function arccosx = myacos;
function arccosx3
  extends myacos;
end arccosx3;

class A
  import arccosx2 = myacos;
  constant Real x = arccosx(0);
  constant Real x2 = arccosx2(0);
  constant Real x3 = arccosx3(0);
end A;

This will generate arccosx and arccosx3. But they will return random memory ;)

[sjoelund.se]

This now generates a warning since it usually gives unexpected behaviour (and the spec doesn't allow inheriting external declarations).