"tab" is doing something funky on my comments

The problem you have is the “5 Most Read Posts via Email” email box and submit button.

Each of the comment fields are set as follows,

Name – tabindex 1
E-Mail – tabindex 2
Website – tabindex 3
Comment – tabindex 4

However, the sidebar email signup fields are set as follows,

E-Mail – tabindex 1
Submit – tabindex 2

So when you press tab from the Comments Name, it moves to the E-Mail box, then to the Comments E-Mail, then to the E-Mail box Submit, then back to Website. It follows the tabindex. So in fact it’s doing as it’s told.

You’ll find the Gform tabindex documentation useful here.