Steps to reproduce:
1. Open attached “ProjectSettings.zip” Unity project
2. Have two Inspector windows open
3. Open Player Settings
4. Enter a new value for Version field in iOS panel
5. Click in Hierarchy/Project window to hide PlayerSettings
6. Open Player Settings again (Repeat from step 4 with the other Inspector window if the value was saved)

Expected results:
Version number has changed to the entered value
Actual results:
Version number was not saved and did not change

Reproduced in: 2018.1.0a5, 2017.3.0b11, 2017.2.0p3, 2017.1.2p3, 5.6.4p3, 5.6.2f1, 5.6.1f1, 5.6.0p1, 5.6.0f2
Didn’t reproduce in: 5.6.0f1, 5.6.0b1

Note: Only happens while editing Version field in iOS PlayerSettings panel with iOS as the target platform.