Steps to reproduce:

1) Open Unity and create a new project
2) Add an empty gameObject in the Hierarchy window
3) In the Inspector window, select X position and change the value, ex: 123
4) Press Tab on the keyboard to switch between input fields for a position value
5) Try to insert any number

Expected result: Input field is switched and opportunity to insert the value should be enabled (check attached video 'expected.mp4')
Actual result: Input field is switched, but there is no way to enter the value (check attached video 'actual.mp4')

Reproduced with:
2017.1.1p3, 2017.2.0f1, 2017.3.0b3

Not reproduced with:
5.6.3p4, 2017.1.1p2, 2017.2.0b11, 2017.3.0a7

Regression since:
2017.1.1p3 - 2017.1.x
2017.2.0f1 - 2017.2.x
2017.3.0b1 - 2017.3.x

Tested on the Windows machine

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Fixed in 2017.3, 2017.2.0p1 and 2017.1.2p3