Reproduction steps:
1. Create new project.
2. Create empty GameObject.
3. Open Timeline windows and create track for selecte object.
4. Press undo.

Expected result: Everything will be removed cleanly.
Actual result: Warning appears: "Component of type Animator was added to GameObject using GameObject.AddComponent() and had become dangling during an undo
operation. Use Undo.AddComponent to correctly add a component which can be handle by the undo system"

Reproduced on: 2017.1.0b6, 2017.2.0a1