To reproduce:
this.radTreeView1.TriStateMode = true;
RadTreeNode sitesNode = radTreeView1.Nodes.Add("Sites", "Sites", "");
sitesNode.Expanded = true;
RadTreeNode siteNode = new RadTreeNode("A site");
sitesNode.Nodes.Add(siteNode);
RadTreeNode eNode = new RadTreeNode("Event Types");
siteNode.Nodes.Add(eNode);
siteNode.Expanded = true;
RadTreeNode dummy = new RadTreeNode("dummy");
eNode.Nodes.Add(dummy);
dummy.CheckState = ToggleState.On;
RadTreeNode dummy2 = new RadTreeNode("dummy2");
eNode.Nodes.Add(dummy2);
dummy2.CheckState = ToggleState.Off;
Please refer to the attached screenshot.
Workaround: change the CheckState property after all nodes are added to RadTreeView.
this.radTreeView1.TriStateMode = true;
RadTreeNode sitesNode = radTreeView1.Nodes.Add("Sites", "Sites", "");
sitesNode.Expanded = true;
RadTreeNode siteNode = new RadTreeNode("A site");
sitesNode.Nodes.Add(siteNode);
RadTreeNode eNode = new RadTreeNode("Event Types");
siteNode.Nodes.Add(eNode);
siteNode.Expanded = true;
RadTreeNode dummy = new RadTreeNode("dummy");
eNode.Nodes.Add(dummy);
RadTreeNode dummy2 = new RadTreeNode("dummy2");
eNode.Nodes.Add(dummy2);
dummy2.CheckState = ToggleState.Off;
dummy.CheckState = ToggleState.On;