Image Mask does not animate according to the "Show Mask Graphic" property's toggle value, although value changes in the inspector.

Steps to repro:
1. Create new or Open attached project
2. GameObject > UI > Image
3. Add Component > UI > Mask
4. Right click in Project Window > Create > Animation
5. Drag animation on a Image
6. Select Image gameobject
7. Window > Animation > Animation
8. Add Property > Mask (Script) > "Show Mask Graphic"
9. Add Animation keyframes with values true and false
10. Play the scene

Note:
1. Refer attached video
2. When the value is toggled via script, it works as it does in the editor. Issue happens only with animation

Actual result:
Image Mask does not animate with respect to the "Show Mask Graphic" property's toggle value.

Expected result:
Image Mask animates with respect to the "Show Mask Graphic" property just like it does when changed in Editor

Reproduced in:
2019.2.0a1, 2019.1.0a14, 2018.3.0f2, 2017.1.5f1

Environment:
Windows & Mac