How to reproduce:
1. Open the user's project
2. In the Project go to Scenes -> SampleScene
3. Enter Play Mode
4. Hold Left Mouse Button on the circle
5. Alt-tab (without moving the circle) to lose focus then alt-tab back into Unity
6. At this point it is safe to release Left Mouse Button, the circle will be dragged without holding it
7. Click Left Mouse Button again to release circle

Expected result: OnEndDrag() is called after releasing the circle
Actual result: OnEndDrag() is not called

Reproducible with: 2017.4.12f1, 2018.1.9f2, 2018.2.10f1, 2018.3.0b3, 2019.1.0a2