Android activity not started if already in the backstack as the root?

I have a sample app with 3 activities: Main, A and B. None of them has any launchMode.

Now I do this:

1. open the app, Main activity is displayed
2. leave the app using back button, so that there is no activity running
3. receive a broadcast which starts a new activity A (new_task flag)
4. open activity B by clicking on a button in activity A (no flags)
5. receive a broadcast which starts a new activity A (new_task flag)
6. new activity A is not started (if I go back, there's still the previous Activity A)

At step #6, activity A should be presented but is not.

If I try to present activity C instead (in #5), it is presented as expected.

If in #2 I leave the app by homebutton instead, everything works as expected.

How is this possible? And how can I ensure that the activity is always presented? I could use FLAG_ACTIVITY_CLEAR_TOP|FLAG_ACTIVITY_SINGLE_TOP, but I want to maintain the backstack.

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