What happened:
Input field is not highlighting while dragging and dropping object in timeline window

Steps to Reproduce
1.Open Unity
2.Create GameObject
3.Select GameObject.
4.Select "Timeline" from Window
5.Create new "Animation track"
6. Input field will generate
7. Drag Gameobject created and try to drop in Animation Track input field
8. Animation track input field should Highlight in drag and drop process.

Expected Result:
Animation track input field doesn't Highlight in drag and drop process.

Frequency: Always

Reproducible with:
2018.1.0a4, 2017.3.0b4, 2017.1.1f1, 2017.1.0f3,2017.3.0b1

Environment: Windows 10, MacOS 10.12
Unity version: Unity 2017.3.0b9
License type: Free