Body font setting in Notational Velocity Settings won't stay set

[mikehamca]

I have (repeatedly) changed the body font size from 12 (the default) to 18 (more readable). The change holds for a while, but eventually, the font size resets itself to 12. I have not been able to find a "Save" button, and perhaps the problem is that I am not saving the new setting. I do click "Set..." and I thought that would make the change permanent, but it doesn't.

Is there any way to permanently set body font size to 18?