Why is My Sites... empty when in fact all the visible sites are also my sites? Doesn't MY SITES describe sites on both lists?
Isn't the My Sites list really the Sites Not Visible as Tabs list? I'd recommend changing the field name to better express the either/or relationship of these two lists.
Not Visible as Tabs
Visible as Tabs
would be parallel yet similar to what's already there. Or maybe
Hide tab for...
Show tab for...
I think a text change here could really improve users' understanding of the relationship between these lists.