Reproduction Steps:
1. Import attached project.
2. Drag "Cube" prefab into the Hierarchy.
3. Change a value of the child object in Transform.
4. Right click on the changed value and select "Revert Value to Prefab".
5. Observe value.

Expected result: Prefab override flag resets on the first reset.
Actual result: After a few seconds, the value fails to reset and becomes bold again. A second revert is required. (GIF attached)

Note #1: The position value of the parent object tends to reset properly.

Note #2: This bug applies to any GameObject value. For example, activating the "Is Trigger" or the "Receive Shadows" values and reverting them to prefab yields the same results.

Reproducible with: 5.5.2p2, 5.6.0f1, 2017.1.0a3

Note #3: The feature is not available in previous versions.

Fixed in 2018.3.0a6