My script does not “activate” stuff when opening.
The checkbox on the left create/remove the string options. The checkbox (and others inputs) on the right set values for string options.
Irradiance particles options are always created by Maya in the miDefaultOptions node (check the String option tab of this node, you will see there is many string options present here).
When you open enjoyMentalRayStringOptions it will set his UI depending on string options you have in your scene.
So if Irradiance particles string options are presents, It “activate” them (checkbox on the left) in his UI. But if you look at the checkbox on the right just after “Irradiance Particles” you will see it is not ticked: Irradiance Particles is actually not “activated” (mental ray will not render with them).
If you remove Irradiance Particles string options (tick checkbox on the left) you will break you render setting panel (because it need this string options to be shown).
This script does not change your string options if you don’t ask him to do it. It’s not a workflow script that take decisions for you. 
Hope this help. 
EDIT: Oh! I think I understand your problem. Maya seems to have callbacks that make what you see in my script wrong… I have no solution (as I never encountered this actually. I just suppose this could be the problem) Just be careful and don’t remove string options Maya need. 
