To reproduce:
1. Open a new Unity project
2. Click on any object in the Hierarchy window to prompt Inspector window
3. In the inspector window, click on any input field
4. press tab to jump to another input field

Expected result: On tabbing to another input field, the value inside it should be selected and you should be able to change the value instantly (see attached gif "tabworks.gif")
Actual result: On tabbing to another input field, the field is highlighted, but the value inside is not selected, you have to make an additional click to be able to change the value (see attached gif "tabdoesnotwork.gif")

Regression first introduced in: 2017.1.1p3
Reproduced on: 2017.1.1p3, 2017.1.2p2. 2017.2.0f1, 2017.2.0f3,
Not reproduced on: 5.6.4p1, 2017.1.1p2, 2017.2.0a1, 2017.2.0b11

Note: Fixed in 2017.3.0b6