Reproduction steps:
1. Create new project.
2. Create empty object and a child for it.
3. Drag it to project window to save as prefab.
4. Press on prefab and add Rect transform to parent.
5. Undo that action.

Expected result: Rect transform will be removed.
Actual result: Unity crashes.

Reproduced on: 5.3.0f4, 5.4.5p2, 5.5.3p3, 5.6.1p1, 2017.1.0b6.
Works fine in 5.2.5f1.