The UI system ignores both values when the default value is specified in the var() function, if the variable is resolvable

Reproduction steps:
1. Open the “USS_variablebug.zip” project
2. Open the “Example.uxml” by double-clicking it in the Project window
3. Observe the Viewport in the UI Builder window

Expected result: The image is yellow-colored
Actual result: The image has no color

Reproducible in: 2021.3.41f1, 2022.3.40f1, 6000.0.12f1

Reproducible on: Windows 11
Not reproducible on: No other environment tested

Note: If the variable value is unresolvable, the default value is used correctly