How to reproduce:
1. Open the attached '1336180.zip' project
2. Open the 'Test' Scene
3. Enter the Play mode
4. Observe the Console
Expected result: No visible errors present
Actual result: Multiple InvalidOperationException errors appear in the Console
Reproducible with: UI Toolkit 1.0.0-preview.4 (2020.2.7f1, 2020.3.12f1, 2021.1.11f1), 2021.2.0a19
Cannot test with: UI Toolkit 1.0.0-preview.13 (2020.3.12f1, 2021.1.11f1) (package errors)