Steps to reproduce:
1. Apply the attached patch to 1.8+.
2. Go to the editing questions screen of any course.
3. Add a new true/false question.
You will see a lot of debugging output on the screen. This comes from code the patch adds to the getValidationScript method which starts on line 993 of formslib.php.
The point to note is that in the first array dumped to screen, element 8 is the 'Penalty factor' Field, while in the last array dumped to the screen, this has got corrupted and replaced by a copy of the 'Default question grade' field.
I have no idea how that happened.
If the issues is that actually I have frozen a required field, then we really need a removeRule method, to complement addRule.