Do you actually mean Checked event instead of Select (SelectionChanged)? I guess you mean that you use the IsInTriStateMode set to true on the RadTreeView. So what happens when you check a parent node and then expand it ?
By design, the RadTreeViewItems are generated initially when they are root level items and all other RadTreeViewItems are generated when their parent is being expanded. So when you expand a node, then its children are generated but their CheckState property does not inherit their parent's CheckState automatically. The "TriState" logic basically works only with already created containers(RadTreeViewItems). The way to workaround this is to use DataBinding with ViewModels and create your own custom Tri-State logic in these viewmodels. You can examine how this could be achieved in this code library project.
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