UI Builder panels become non-resizable when width is narrowed and UI Builder is not maximized

Steps to reproduce:

1. Create a new project using Universal 3D template
2. Go to Assets > Create > UI Toolkit > UI Document (UXML)
3. Open the created UI Document in UI Builder (make sure UI Builder is not maximized)
4. Resize the left UI Builder panel to as narrow as possible
5. Try to resize the same panel or UI Builder Inspector again

Actual results: the panels/windows are not resizable

Expected results: The panels/windows resize on drag

Reproducible with versions: 6000.3.0a1, 6000.3.8f1, 6000.4.0b8, 6000.5.0a6

Not reproducible with versions: 6000.0.66f1, 6000.2.0b2

Reproducible on: Ubuntu 24.04, Ubuntu 22.04
Not reproducible on: Windows 11, macOS 26.2

Notes:

• The issue could be inconsistent to reproduce. If it doesn't reproduce instantly, try adding elements to the Hierarchy and saving or resetting the UI Builder layout
• Does not reproduce if the UI Builder window is maximized