Reproduction steps:
1. Open the attached “IN-112625.zip” project
2. From the Project Window, open the “NewUXMLTemplate.uxml” asset in UI Builder
3. From the Hierarchy, select the “#Label” element
4. In the Inspector, expand the Text foldout and find the Color property
5. Click on the color picker
6. Click anywhere inside the viewport
7. Move the mouse
8. Repeat the 5-7th steps a few times until reproduced
9. Observe the UI Builder window

Expected result: UI Builder window does not move
Actual result: UI Builder window moves/snaps to a different location

Reproducible with: 6000.3.0a1, 6000.3.0a6
Not reproducible with: 6000.0.56f1, 6000.2.0b2, 6000.2.2f1

Reproducible on: Windows 11
Not reproducible on: no other environments tested

Note:
- With the earlier versions (6000.3.0a1 - 6000.3.0a4), the reproduction is even more inconsistent and occurs around once in 10-20 times

UPDATE:

This only repros if you click at about the center of the screen. Clicking with the mouse elsewhere on the screen doesn't cause the issue.