How to reproduce:
1. Create empty Unity project
2. Create ScriptableObject script with at least one public field and make it creatable from the menu
3. Create ScriptableObject
4. Lock it in the inspector
5. Make sure game window is checked maximize on play
6. Enter play mode
7. Pause the game
8. Inspector is unlocked

Expected result: Inspector should remain locked all the time
Actual result: Inspector became unlocked after entering the play mode

Regression first introduced in: 2018.1.0b7
Reproducible with: 2018.3.0a1, 2018.2.0b4, 2018.1.0f2,
Not reproducible with: 2017.4.3f1, 2017.3.2f1, 2017.2.2p2, 2017.1.4f1

Note:
Bug similar to 1031140 but it can be reproduced with different versions