Radio Button Group "Choices" size drops to 0 when saving a UXML file with empty choice elements

How to reproduce:

1. Create an empty project and open it
2. In the top bar of Unity Editor, select “Window” > “UI Toolkit” > “UI Builder”
3. In the UI Builder window, drag “Radio Button Group” from the Library tab into “< unsaved file >.uxml” in the Hierarchy tab
4. In UI Builder Hierarchy, select the “< unsaved file >.uxml” and save it (Ctrl + S)
5. In UI Builder Hierarchy, select “RadioButtonGroup”
6. In UI Builder Inspector under Attributes, change “Choices” size to 3
7. In UI Builder Inspector, click on the empty space to load the elements (leave the elements empty)
8. Save the changes (Ctrl + S) and observe the results in UI Builder Inspector and in the UI Builder Viewport

Actual result: The “Choices” size drops to 0 and the radio buttons disappear from the Viewport after saving
Expected result: The “Choices” size is 3 and radio buttons are shown in the Viewport after saving

Reproducible with: 6000.0.1f1, 6000.0.81f1, 6000.3.22f1, 6000.5.8f1, 6000.6.0b8, 6000.7.0a4

Reproducible on: Windows 11 Enterprise (25H2)
Not reproducible on: No other environments tested

Workaround: Fill the “Choices” elements with values and then save (Ctrl + S)