I was previously using clearTask in my navigation actions to make sure that the user could not navigate back to the previous destination (useful for splash screens and login screens). After it was deprecated I decided to try the recommended approach of instead setting popUpTo pointing to the root of the graph together with setting popUpToInclusive="true", but this didn't have the effect I wanted.

This approach only seem to work on actions originating from the graph's start destination, and fails on actions between any other destinations. I created a sample project which reproduces the issue:
https://github.com/hsson/android-navigation-component-alpha06-bug

Here is the project's README detailing the issue:

# Bug in Android Navigation Component (alpha06)
(Note: I have only verified this in alpha06, I don't know if it exists in
previous versions)

## The problem
Basically the problem is that the NavOption "clearTask" was removed in
alpha02, and the recommended substitute was to use app:popUpTo pointing to
the root of the graph/the graph ID, together with app:popUpToInclusive="true".
However, this method does not work. It only seems to work for actions
going from the graph's start destination. If we have the following graph:

x y
A ---> B ---> C

Where A, B, and C are fragments, A is the start destination of the grapg,
and x, y are actions going from A to B and B to C respectively. Let's say
the graph's ID is "@+id/graph"

Then, if both actions x and y have
app:popUpTo="@+id/graph"
app:popUpToInclusive="true"

Then when navigating from A to B through x, and then hitting the back button
will exit the app (as expected). But if navigating from A to B to C through
x and y, and then hitting the back button we will navigate back to B — this
is not what was expected. The expected behavior with this graph is to always
exit the app when clicking the back button

## Environment
This was verified using:
Android Studio 3.2 RC 3
Build #AI-181.5540.7.32.4987877, built on August 31, 2018
JRE: 1.8.0_152-release-1136-b06 x86_64
JVM: OpenJDK 64-Bit Server VM by JetBrains s.r.o
macOS 10.13.6