Android heads-up notification not showing after disable and enable it on application settings

I made heads up notification on my application and it's working well.
But when I disable -> enable it on my application notification settings, I can not see heads up notification anymore.
(It still shows on notification bar, makes sound and vibration, but not on heads-up)

-- The logcat message says.

• before disable/enable it
  showForNotification : isInteractive=true, isHeadUp=true, color=0, sbn = StatusBarNotification...

• after disable/enable it
  showForNotification : isInteractive=true, isHeadUp=false, color=0, sbn = StatusBarNotification...

This issue is not resolved when the app is killed and restarted.
Only works normally again when app is deleted and reinstalled.

Is there any way to solve it?

Thanks for your time.

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Edited

I found same issue on sample code
https://github.com/googlearchive/android-Notifications

In this application, set notification style to BIG_PICTURE_STYLE and press launch button. then, you can see heads-up notification, but after set "Sample Social" notification settings off -> on from application notification settings, you can not see heads-up notification anymore.

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