Reproduction steps:
1. Open the attached project “NotSavedUXML”
2. In the Viewport window select the Quests button
3. From the Project window, attach the “IconPath” to a property “Icon Image” located in UI Builder’s Inspector
4. Save the Project
5. Observe the UI Builder’s Viewport window

Expected result: The state of the “MainMenu.uxml” stays the same
Actual result: Changes to the “MainMenu.uxml” get reverted

Reproducible with: 2023.2.0a17
Couldn’t test with: 2021.3.27f1, 2022.3.3f1, 2023.1.1f1 (Can’t add Icons to the button)
Fixed with: 2023.2.0a18

Reproducible on: Windows 10
Not reproducible on: Intel MacOS Ventura 13.3.1

Notes:
If it doesn’t reproduce with the Quests button, then attach icons to other buttons as well
In step 3, other icons can also be used
Reimporting the “Assets/UI/MainMenu/MainMenu.uxml” file will revert changes as well