Reproduction steps:
1. Open the 'UI Tookit theme bug' project
2. Open the 'theme1' file in any text editor
3. Make any small change and save the file
4. In Unity Editor enter Play mode
5. Hover the green square with a cursor a few times

Expected result: animation is played (red square slowly hovers the green one) every time
Actual result: animation transaction works correctly only once; after hovering the green square with the cursor for the second time the red square covers the green one immediately

Reproducible with: 1.0.0 (2021.2.0f1, 2021.2.3f1)
Not reproducible with: 1.0.0 (2021.2.0b1, 2021.2.0b16, 2022.1.0a1, 2022.1.0a15)
Could not test with: 1.0.0 (earlier 2021.2.0a21 - multiple errors), 1.0.0 (2019.4.32f1 - no UI Toolkit)

Note: if the 'testTheme' file is always changed only in the UI Builder animation transition works correctly; after saving in a text editor the issue starts happening