How to reproduce:
1. Create and open a new project
2. Create a new UI Document
3. Add a Multi-Column List View element to the Hierarchy
4. Select the newly Created visual element
5. In the Inspector, Attributes section, find and expand Columns fields
6. Click the “+” twice to add two columns
7. Select the last created column
8. Press “-” to remove the element
9. Repeat step 8 without selecting the other element
10. Observe the list and the Console
Actual result: The first column is not removed from the list and an error is thrown in the Console
Expected result: The column is removed, no errors are thrown
Reproducible with: 6000.0.1f1, 6000.0.75f1, 6000.3.16f1, 6000.4.8f1, 6000.5.0b9
Not reproducible with: 6000.0.0f1 (4ff56b3ea44c), 6000.6.0a5
Fixed in: 6000.6.0a1
Reproducible on: macOS 26.4 (M1 Pro)
Not reproducible on: No other environments tested