I couldn't reproduce the odd behavior you're describing in the navigation widget, but since browser's AutoComplete functionality is the same everywhere on the website, I've recorded a video
on the way it works when someone logs in to Sitefinity. As you see changes are applied even when I use the mouse and select from the dropdown.
the Telerik team
Do you want to have your say in the Sitefinity development roadmap? Do you want to know when a feature you requested is added or when a bug fixed? Explore the Telerik Public Issue Tracking
system and vote to affect the priority of the items