Could you see what happens when you click the back button in the browser?
It could also look as if you were logged out because the page closes when you press the save/cancel button.
Each dataview has an option "close on save&cancel", when you click the button it closes the dataview. But if there is nothing to go back to it might seem as if you logged out, but if you go back directly to index.html you might still have an active session.
Normally when you browse through the app you can use the back button from the browser to navigate back, so you can check what happens when you click the back button. If you are 'logged out' that way too, it is caused because of the earlier mentioned property, "close on save&cancel".
The solution would be either to change the property to false, or don't close the previous page when navigating to your dataview.