Google just published their new Android Design site and I think that's mostly a good thing. Unfortunately they put one item in writing that I was hoping was a bug in their apps and not a conscious design decision.

At the bottom of the Navigation page, it states that For the Back key, you should make navigation more predictably by inserting into the task's back stack the complete upward navigation path to the app's topmost screen. This way, a user who has forgotten how they entered your app can safely navigate to the app's topmost screen before exiting it. I absolutely hate this advice as it's a constant workflow annoyance and seems different than the intended purpose of the back stack while at the same time making the back button less predictable.

For example, when you get a new email notification and tap on it, you're looking at the message the notification was for... so far, so good. However, when you're done you tap the back button expecting to go back to wherever you were before tapping on the notification. Instead, you find that now you're in the main email activity that was not even part of the original workflow. So now you have to hit the back button again to get to where you were before tapping the notification. One tap to get in, two taps to get out... intuitive, huh?

OK, so this is something they explicitly want developers to do as well. To not follow this recommendation would probably confuse users as it would result in inconsistent behavior across apps. So my thinking right now is that I'll probably do it but I won't like it. However, if I do I'll also put a setting allowing for this behavior to be disabled for any like-minded users who don't care for this behavior. Hopefully other developers will do the same.

Update 7/3/2012: Based on the Navigation in Android presentation from Google I/O 2012, the rationale behind the back stack override is making more sense to me. What I was missing was the desired hub and spoke model re: the home screen and an attempt to anchor things like notifications within that model. I can see how this would result in an easier to use and understand system for users.