First off, nice looking form! Second off, you are not crazy -- I am seeing exactly the same thing on my machine. I started a new blank form for comparison and added two optional section, making the ability to add / remove one dependent upon the presence of the other (like you have in your form) and it worked beautifully. On your form, I added some expression boxes with the conditional formatting requirements for section 2 -- when all 4 evaluated to false, I anticipated the conditional formatting would not apply and I'd be able to add section 2 -- no luck.
However, when I copied section 1 and 2 into a new view in the same form, the conditional formatting worked as I'd anticipate. That makes me think there is some other rule or condition in the form causing your issue. You may want to try this -- create a new view, and start copying your sections over, previewing as you go, watching to see when things stop working....