1. Create a new project and add empty RadTreeView when handling its Form.Load event.
2. Set its AutoSize property to true.
3. Run the project.

To reproduce: Add a RadTreeView with hierarchical data. Select a node with hierarchy level > 0. Call the Clear method of the Nodes collection. Refill the tree, drag and drop a node, you will see that two nodes will be dropped since the previous node's Selected property is set to true. 

Workaround: private void DetachAllNodes(RadTreeNode parent) { this.CleanNode(parent); foreach (RadTreeNode node in parent.Nodes) { this.DetachAllNodes(node); } } private void CleanNode(RadTreeNode node) { node.Current = false; node.Selected = false; } foreach (RadTreeNode node in tree.Nodes) { this.DetachAllNodes(node); } tree.Nodes.Clear();

FIX. RadTreeView - the GradientStyle property of RadTreeNode is overriden by the theme, even though it is set locally
The first part of the issue, regarding RadTreeNode.BackColor is addressed.
There is no issue with the persistance of GradientStyle property. To persist the GradientStyle property you should set its value explicitly. Here is an example:
void radTreeView1_NodeFormatting(object sender, TreeNodeFormattingEventArgs e)
{
if (radTreeView1.SelectedNode != null)
{
if (e.Node == radTreeView1.SelectedNode)
{
e.NodeElement.BackColor = Color.Yellow;
e.NodeElement.BackColor2 = Color.White;
e.NodeElement.GradientStyle = Telerik.WinControls.GradientStyles.Linear;
e.NodeElement.DrawFill = true;
e.NodeElement.NumberOfColors = 2;
return;
}
}
e.NodeElement.ResetValue(LightVisualElement.BackColorProperty, Telerik.WinControls.ValueResetFlags.Local);
e.NodeElement.ResetValue(LightVisualElement.BackColor2Property, Telerik.WinControls.ValueResetFlags.Local);
e.NodeElement.ResetValue(LightVisualElement.GradientStyleProperty, Telerik.WinControls.ValueResetFlags.Local);
e.NodeElement.ResetValue(LightVisualElement.DrawFillProperty, Telerik.WinControls.ValueResetFlags.Local);
e.NodeElement.ResetValue(LightVisualElement.NumberOfColorsProperty, Telerik.WinControls.ValueResetFlags.Local);
}

FIX. RadTreeView - Collapse method of RadTreeNode throws an exception if uised afrer children are added

The images and SignStyle cannot be modified using Visual Style Builder.