To reproduce:

1. Download attached project "TaskDelay.zip" and open in Unity
2. Open "SampleScene" scene
3. Select "TDelay" gameObject in Hierarchy and in Inspector window set "Millis Delay to 21 or bigger
4. Enter Play mode
5. Press the "C" button in keyboard
6. Observe that in Console returned value of "Token.IsCancellationRequested" is false as expected before the "TaskCanceledException" is thrown
7. Exit Play mode
8. Select "TDelay" gameObject in Hierarchy and in Inspector window set "Millis Delay to 20 or less
9. Enter Play mode
10. Press the "C" button in keyboard
11. Observe that in Console returned value of "Token.IsCancellationRequested" is true before the "TaskCanceledException" is thrown

Notes:
- This issue appears on both Windows and OSX
- In VisualStudio 2017 the returned value of "Token.IsCancellationRequested" is always false even if "millisDelay" = 1

Reproduced on Unity 2018.2.0b3, 2018.2.8f1, 2018.3.0b2 and 2019.1.0a1
Not reproduced on Unity 2018.2.0b2 (96999d86066c)
Regression on Unity 2018.2.0b3 (0a6b93065060)