The sync namespace is a refactor option that you have to opt into. I don't see the behavior you see when I move a file to a new folder. It retains the old namespace name like I'd expect. There was pushback about making this automatic for the very reasons you mentioned, amongst others so it was opt in.
Unfortunately the paste command doesn't expose which refactors it'll do and I believe it is tied to code cleanup which itself is tied to format document so it gets ugly fast. Some things that come to mind as to what might be causing this for you:
- Your editorconfig has enabled this feature (not sure if it is available there yet)
- You have some other extension installed (like ReSharper or CodeRush) that is actually running the code cleanup tools
- A setting in the MAUI project properties has this feature turned on. Try doing this same thing on a console/class library project and see if the problem still occurs. If it does then it is VS wide otherwise it might just be tied to the project settings.
Unfortunately I don't know a great way of diagnosing what is triggering the code cleanup rules (which I believe is what is causing this issue for you).