Unset attributes on Multi Column List View and Multi Column Tree View revert to type default values when the .uxml is saved in in-scene UI Authoring

Steps to reproduce:

1. Create a new Unity project using the Universal 3D template
2. Right-click in the Hierarchy > UI Toolkit > Standard Elements > UI Library
3. Double click the "Multi Column List View" or "Multi Column Tree View" to add it and save the .uxml in project
4. In the Inspector, observe that Stretch Mode is "Grow And Fill" and that Reorderable and Resizable are enabled
5. Expand the Columns > Columns foldout and add one Column using the "+" button
6. Expand the new Column and observe that Visible, Sortable, Optional and Resizable are enabled and Min Width Value is 35
7. Save the .uxml
8. Observe the same properties in the Inspector

Actual results: Unset attributes revert to type default values after saving - become unchecked or go back to "0" value

Expected results: Unset attributes keep their declared default values after saving

Reproducible with versions: 6000.6.0b2, 6000.6.0b7, 6000.7.0a4

Can’t test with versions: 6000.3.21f1, 6000.5.7f1 (in-scene UI Authoring not available)

Tested on (OS): Windows 11

Notes:

• Reproduces only in in-scene UI Authoring. Editing and saving the same document in the UI Builder window is not affected - the default values persist correctly there
• Manually enabling a property writes it explicitly to the .uxml, after which it persists correctly