A "Cannot save invalid window Create Layout" warning is thrown when any custom layout is created

How to reproduce:

1. Create and open a new project
2. Create a new Editor Layout (Layout → Save Layout → [enter name] → Create)
3. Observe the Console

Actual result: A “Cannot save invalid window Create Layout (UnityEditor.PromptWindow) to layout“ warning is thrown, but the layout is created
Expected result: Nothing is thrown, and the layout is created

Reproducible in: 6000.3.3f1, 6000.4.0a3, 6000.4.0b3, 6000.5.0a4
Not reproducible in: 6000.0.65f1, 6000.4.0a2 (79bd4f638ac0)

Reproduced on: Windows 11 Pro (25H2)
Not reproduced on: No other environment tested

Notes:

• The Layout gets saved and usable on the same instance of the Editor
• Other users report the layouts getting corrupted after the Editor is closed with the following error: “You may not pass in objects that are already persistent” (unable to reproduce locally)