UI is stuck to the viewport window when panning in the UI Viewport opened via "Open In Context"

Steps to reproduce:

1. Create and open a new project
2. Import the "BackdropDemo.uss" and "BackdropDemo.uxml" into the Project
3. In Edit -> Project Settings -> UI Toolkit, enable 'Enable in-scene UI Authoring'
4. Instantiate the UXML in the scene and select the 'BackdropDemo.uxml' child GameObject
5. Press "Open In Context" in the Inspector
6. Pan around in the opened UI Viewport and observe

Actual results: UI is stuck to the viewport window

Expected results: UI is displayed inside the checkered canvas

Reproducible with versions: 6000.6.0b1, 6000.7.0a1

Can’t test with versions: 6000.0.77f1, 6000.3.18f1, 6000.5.1f1, 6000.6.0a7 (No UI Viewport)

Tested on (OS): Windows 11 Pro (25H2)

Notes:

• Does not reproduce in UI Builder, or if the UI Viewport is opened by entering through the right arrow in Hierarchy