[fpc-pascal] const parameter writeable

[L505]

Are const parameters supposed to ensure read only access?
If so how come one can write to a typed pointer?

program project1;

{$mode objfpc}{$H+}

  type
    PSomeRec = ^TSomeRec;
    TSomeRec = record
      a: string;
      b: string;
    end;

  procedure ChangeRec1(const Rec: PSomeRec);
  begin
    Rec^.a:= 'string A';
  end;

var
  RecPtr: PSomeRec;
begin
  new(RecPtr);
  ChangeRec1(RecPtr);
  writeln(RecPtr^.a);
  dispose(RecPtr);
  readln;
end.