How to reproduce (Not reproduced by Customer QA):

1. Create and open a new project
2. Create a new UXML file and open it in UI Builder
3. Add any element to the UI Builder Hierarchy
4. Expand ‘Text → Shadow’ in the UI Builder Inspector
5. Drag any label (under the ‘Shadow’ section) sideways to change the value
6. Observe the UI Builder Inspector

Actual result: The new value is appended to the old one
Expected result: The old value is overwritten with a new one

Reproducible in: 6000.2.12f1, 6000.3.0b10
Not reproducible in: 6000.0.62f1

Reproduced on: Windows 10 (10.0.19045) X64 (by the reporter)
Not reproduced on: Windows 11 Pro (25H2) X64

Note: Seemingly, only the Text Shadow subsection values are affected