If you manually remove entry from qmldir file without touching the corresponding .qml document while the project is open, exportedTypeNamesChanged doesn't trigger and type still works in editor (e.g. you can see and modify properties), but you can't run the project. If you reload the project, type doesn't work.

If you delete the entire qmldir file, you get exportedTypeNamesChanged for the types in there, but if you then undo the deletion of qmldir file, there are no notifications about the types being added again and the types do not work in the editor.