Tooltips are missing for track switcher and settings button

Steps to Repro:
1. Create a new Project
2. Window > Sequencing > Timeline
3. Hierarchy > Select a GameObject
4. Create a timeline track
5. Hover over settings button
6. Hover over track button

Actual Result:
Tooltips are missing

Expected Result:
tooltips are displayed

Occurring with:
2019.3.0a2, 2019.2.0b1, 2019.1.0f2, 2018.1.9f2, 2017.4.17f1

Environment:
Windows and Mac