Setting a variable in the root selector via an imported USS file in a theme does not work

How to reproduce:

1. Open the “ScrollingBug.zip“ project
2. Open the “SampleScene“
3. Enter Play Mode
4. Scroll in the List view in the Game view
5. Press the “Toggle line height“ button
6. Scroll in the List view in the Game view again and observe

Actual result: List view scrolls very slowly
Expected result: List view scrolls just like in step 4

Reproducible in: 6000.0.64f1, 6000.3.0a6, 6000.3.1f1, 6000.4.0b1, 6000.5.0a3
Could not test in: 6000.3.0a5 (36d7e9fd6645) (The issue was not fixed at all, so there is no scrolling speed difference)

Reproduced on: Windows 11 Pro (24H2)
Not reproduced on: No other environment tested

Notes:

• The "--unity-metrics-single_line-height" value is passed in through the TTS file
• In the TTS file, a different value for "--unity-metrics-single_line-height" will change how slow the scrolling is
• In version 6000.3.0a6 and later, and in the backported streams, the issue [Internal link] is partially fixed - in this case, as an example, scrolling speed is altered only when the selector is added to the class list, but not by default on the root selector imported via a USS file in a theme