BottomNavigationBar button "pressed" animation is left on screen permanently if you press and hold down a button in the BottomNavigationBar and then press the device's Home button at the same time.

Steps to reproduce the issue using the Flutter Gallery app:

1. Select from menu Material => Bottom Navigation
2. Press and hold down any button in the bottom navigation bar
3. Press the device's Home button at the same time
4. Go back to the Flutter Gallery app.
5. You will see something like this:

So the navigation bar button animation is still in view even though you don't press the button anymore. Animation is removed only after you navigate to some other view.

I can reproduce the same issue with my own app (so this is not Gallery app specific issue) and it happens often also by accident even if I don't actually try to reproduce the issue. I can also reproduce the same issue occasionally using other device buttons.

Test device: Samsung Galaxy S7 / Android 8
Gallery app version January 2019