Nested UI Panels overlap while creating a Prefab of Container Canvas object, where UI Panels have "TextMeshPro" text as child.

Steps to Reproduce:
1. Create a new Project.
2. Add TeshMeshPro from Unity Asset Store.
3. Create a UICanvas.
4. Add a UI Panel as its child.
5. Resize Panel to half of Canvas size.
6. Add TextMeshPro Text as a child of Panel.
7. Create a new Panel as a child of the first Panel.
8. Change position of new Panel so that they don't overlap each other.
9. Add a new TextMeshPro text as a child of newly created Panel.
10. Now try creating Prefab of the Canvas.

Note: Both Panel will overlap in the Scene View.

See attached video for more details.

Notes:
- Appears on both Mac and Windows.
- Appears always

Reproducing on: 2017.3.0b9

Working fine on: 2017.2.0f1 , 2018.1.0a2

Regression on: 2017.3.0b9