I will try to explain the functionality I am looking for a little better. Suppose I have a tabstrip with 3 pages.  Page A, B and C. Page C is an info page and doesn't have sub pages, but Page A and B have a button (or listview) to navigate to a sub page (view) of page A (A-sub) and B (B-sub).

Desired behaviour (IMHO):
Example 1:
When I start the App, it will always show page A. I can click on the Icon for page B to navigate to page B and then click page C to navigate to page C. Now (when I am still on page C) I click the back-button, the app navigates back to page B and when I click the back-button again, I will then navigate from page B to page A. In my example (and in the apps I so far have been working on), I consider the tabs (pages) on the tablist as a menu and when I click the back button I don't want to go to a previous visited page, but I want to exit (with or without warning) the app.

Example 2:
Now I start again, still on page A of course. On page A I have a button that navigates me to a sub page (A-sub). I click the button and the sub-page shows. When I click the back button I want me app to navigate back to page A from sub-A. When I click the back button on page A again, I want to leave the app.

Example 3:
Start the App and page A shows. I click the tab to navigate to page B. On page B there is a list with product categories. I click one of the categories which makes me go to B-sub where the products for that category are shown. Clicking the back button would bring me back to page B. Another back-click would allow me to exit the app.

Example 4 (the last one):
Start the App and page A shows. I click the tab to navigate to page B. On page B there is a list with product categories. I click one of the categories which makes me go to B-sub where the products for that category are shown. Now I click the tab for page A, which makes me navigate to page A. Clicking the back-button this time would ask me to exit the App.

In short: I see the pages belonging to the pages on the tabstrip as parent pages. When one of these pages is currently shown, the back button should close the app. No matter what previous navigation you have done. When on a child  page (navigated from a parent page) and clicking the back-button (either hardware or software) will make you go back to it's parent page.