Hello Leon Williams,
We append this QueryString - locknavigation=true
when you are in the backend and you click on any node of the SiteMap. The QueryString is not visible in the url. Most probably you have some code in your template or any of the page that somehow interacts with the url QueryString. Try creating a simple page and template without any controls on them and see whether the problem will appear. If not, try excluding the controls that you have on the problematic page one by one. Also, I am not sure which "OK" button you are referring.
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