Some UI Toolkit pixels are transparent when not all corners are rounded

How to reproduce:

1. Open the “Reproductions.zip“ project
2. Open the “SampleScene“
3. Create a “UI Document” GameObject in the Hierarchy
4. Assign the appropriate Panel Settings and “WindowTemplate“ UXML as Source Asset
5. Unpause the Play Mode
6. Slowly resize the Game view horizontally and observe the header bar at the top

Expected result: All pixels are always rendered
Actual result: Sometimes 1 or more pixels fail to render when the Game view is at a certain width

Reproducible in: 2023.1.0a1, 6000.0.59f1, 6000.2.7f1, 6000.3.0b4, 6000.4.0a1

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

Notes:

• The pixels are not the physical screen pixels, but the pixels that are rendered by the UI Toolkit
• The behavior can be observed in the UI Builder window as well
• Reproducible in Play Mode, but not reproducible in the Player
• The issue can be tedious to reproduce, but it will almost always reproduce