Changing the GameObject rotation causes the LODGroup bounds to become outdated and the LODGroup UI displays a "Recalculate Bounds" button.
Looking at the actual data of the LODGroup gives the impression it's more of a precision issue than actual outdated bounds. The LODGroup "Size" property changes from "1" to "1.000001" if I press "Recalculate Bounds".

To reproduce:

1. Download attached project “BugReport_LODGroup.zip" and open in Unity
2. Open “Scene” scene
3. Select "Cube" in Hierarchy and duplicate it
4. Select the duplicated Cube GameObject
5. Change Transform Rotation to 571.3
6. Notice the "Recalculate Bounds" button gets enabled
7. Click "Recalculate Bounds"
8. Switch the Inspector to "Debug" mode
9. Observe the "Size" property is 1.000001 rather than 1 like in the original gameObject

Expected results: Changing the GameObject Transform should not cause the LOGGroup Bounds to get outdated
Actual results: Bounds become outdated, because of what seems to be a precision issue. Size changes from 1.0 to 1.000001

Notes:
- This issue appears on both Windows and macOS
- This behavior causes thousands of LODGroups to become outdated while working on an actual level.
- Workaround: You can use UnityEngine.LODUtility.CalculateLODGroupBoundingBox() to fix all these outdated bounds at once

Reproduced on Unity 2017.4.0f1, 2017.4.17f1, 2018.2.20f1, 2018.3.1f1 and 2019.1.0a12