Screen does not always stay on

I love the fact that the app does not let the screen turn off when I have a book open.  This feature does not seem to always work though.  I thought for a while that it was a random problem, but I am starting to think that it might be that this feature does not work after I have backgrounded logos and then come back to it.  Am I missing a setting somewhere or is anyone else experiencing this problem? I am using the latest logos app on my iPhone 4.

-chris