[NB] using the inspector to change multiple section types doesn't work

If I select multiple documents in the binder and right click, select Section Type, and change the section type, they all get changed. But if I change them in the Inspector Section type: dropdown, only the last one clicked gets changed.

I’m on Windows 10 Pro.

This is the intended design; the inspector only ever shows the metadata for a single focussed document in the editor, and thus editing the metadata there will only affect that one document. To change the section type for multiple documents, using the context menu as you did is the way to do it. That works in the binder, outliner, or corkboard.