Storyboard Global Mute property changes on changing the property in its preset asset and vice versa.

Steps to repro:
Create a new project.
1. Window > Package Manager > Cinemachine (2.6.0-preview.5) > Install.
2. Cinemachine menu > Virtual Camera > Extension > Add Extension > CinemachineStoryboard.
3. Create its Preset > CinemachineStoryboard.
4. Inspector > enable/disable Storyboard Global Mute.

Actual Result:
Storyboard Global Mute property changes on changing the property in its preset asset.

Expected Result:
Storyboard Global Mute property should not be changed.

Reproducible in:
2020.2.0a13, 2020.1.0b11, 2019.3.15f1, 2019.2.0f1, 2019.1.0f1, 2018.4.0f1 with Package version 2.6.0-preview.5, 2.5.0, 2.4.0

Note:
-"Storyboard Global Mute" feature introduced in Package version 2.4.0.
-Package version 2.4.0 is introduced in 2018.4.0f1.

Environment:
Occurring on Windows 10 & Mac 10.15.