How to reproduce:
1. Create a new project and create a text object in the Hierarchy Window
2. Drag the text object to the Project Window to create a prefab
3. Open the prefab and change its RectTransform Width to 250
4. Save and exit the prefab mode
5. Observe the text object in the Hierarchy Window

Expected result: The changes are synced, the Hierarchy Window's text prefab has its RectTransform Width set to 250
Actual result: The changes are not synced and nothing changed with the Hierarchy Window text object

Reproduced in: 2019.1.0a7, 2018.3.0b8