Application Express :: Submitting A Page Via Tabs

Isn't it the case that clicking on a tab submits the current page, using the tab name as the request? I'm getting it to work some of the time but not always. In particular, it seems to work if the execution point is "On submission before computation" but not when the execution point is "After submission".

Here is what I did: I created a new application with two pages, each of which has a tab. Page 2 has nothing in it. Page 1 has an item, a button and two PL/SQL processes. Process 1 is unconditional, and sets the item to 10. Process 2 is conditional on the tab named "T_PAGE2", and increments the item by 5.

If both processes execute "on submission before computation" then everything works correctly:
-- If I click on the button, then the item is 10, indicating that only process 1 fired.
-- If I click on the tab to page 2, then the item is 15, indicating that both processes fired.

Now suppose I change them so that the processes execute "after submit". Then the button still works, but the tab doesn't:
-- If I click on the button, then the item is 10, as it should be.
-- If I reset the item value to 0 and click on the tab to page 2, then the item doesn't change, indicating that neither process fired.

Note that I have no computations or validations in my application. My only conclusion is that when you submit via a tab, there is some sort of internal validation occurring that keeps the processes from firing.