Steps to reproduce:

1. Setup perforce server
2. Enable exclusive checkout for prefab and its .meta in p4v
3. Submit change to server and sync projects on both machines
4. Checkout prefab on remote machine
5. Try to checkout prefab on local machine and notice that it fails as expected
6. Add prefab to scene and change its scale
7. Apply changes
8. Notice same error that file couldn't be checked out
- However, notice that prefabs scale is still applied and change is written to disk

Same issue happens to scene files etc, anything that has custom editor

Reproduced with: 2017.4.1f1, 2018.1.0f1, 2018.2.0b1