In the demo you linked the TreeView is filtered by hiding the nodes that do not match the search criteria, that is those nodes are still there but are invisible. We do not have a workaround for this scenario so we would suggest you to consider a different approach for filtering the nodes, one that is shown in the TreeView in Dialog
demo (part of the Dialog demos). In this demo instead of hiding the nodes the widget's dataSource is filtered. This way nodes that do not match the search criteria are not rendered and the keyboard navigation is not obstructed when the TreeView is filtered.