Reproduction steps:
1) Download and open "914823_reproproj.zip"
2) Build and run "main.unity" scene on an Android device
3) Press on any input field
-- Notice that virtual keyboard pops up
4) Press on another input field

Actual result:
Keyboard disappears and the input field is not selected. You have to press on it once again to open keyboard and type in text

Expected result:
Same as in native Android applications: if keyboard is open and you press on another input field - keyboard stays and field into which text is being written changes accordingly

Reproduced with:
5.3.8f1, 5.4.5p3, 5.53p3, 5.6.1p2, 2017.1.0b9

Devices under test:
Samsung Galaxy S8, Android 7
LG G3, Android 5.0
Samsung Galaxy S7, Android 6.0

Devices under test (unable to reproduce):
iPhone SE