How to reproduce:

1. Create and open a new project
2. Create a new UI Toolkit → UI Document in the Project tab
3. Double-click it to open it in UI Builder
4. Add two Visual Elements and select the first added Visual Element
5. In the top right of the UI Builder’s Inspector, rename the Visual Element to anything
6. Without pressing Enter, press CTRL + S to save the changes
7. Observe the Console

Expected result: The new name is validated and saved automatically
Actual result: A UI Document parsing error dialog box pops up, and when dismissed, two “Index was outside of bounds of the array” errors are thrown

Reproducible in: 6000.0.0b12, 6000.0.62f1, 6000.2.11f1, 6000.3.0b9, 6000.4.0a4
Not reproducible in: 6000.0.0b11

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

Notes:
- Afterward, the UXML becomes unusable - no element can be added to the Hierarchy, and “Index was outside of bounds of the array” errors are constantly being spewed out on any change made to the UXML
- Opening the UXML after the reproduction always throws one “Invalid UXML or USS: System.IndexOutOfRangeException: Index was outside the bounds of the array.” error
- The problem cannot be reproduced if the project is created in 6000.2.0a4 for some reason. Only downgrading from 6000.4.0a4 (and maybe some other versions) will yield actual results