Channel Remapping dropdown does not expand on clicking on its text in Mask Map under Terrain Layer.

Steps to repro:
1. Create a new project.
2. Project Window > Click on "+" > Terrain Layer.
3. Select Terrain Layer > Inspector > Assign Mask Map.
4. Click on "Channel Remapping" text.

Actual Result:
Channel Remapping dropdown does not expand on clicking on its text.

Expected Result:
Channel Remapping dropdown should expand on clicking on its text.

Reproducible in:
2020.2.0b7, 2020.1.0a5.

Working Fine in:
2020.1.0a4

Environment:
Occurring on Windows 10 & Mac 10.15.