RadTreeView with virtualization turned on, defines HierarchicalDataTemplates for its items. 

In the template, the root panel is 32 pixels (or higher than the default TreeViewItemHeight - 24 px in OfficeBlackTheme). Scrolling the treeview, then maximizing the wpf window results in misplaced / incorrect height of treeviewitems.

Possible workaround:
Set the MinHeight property of RadTreeViewItem so that all its header content fits. Then set the item's VerticalContentAlignment to Stretch
        <Style TargetType="telerik:RadTreeViewItem">
                         <Setter Property="MinHeight" Value="48" />
                        <Setter Property="VerticalContentAlignment" Value="Stretch" />
                   </Style>

Also following settings might help:
   - setting fixed width/height of the RadTreeView
   - setting ChildDefaultLength to 48 of every TreeviewPanel:
			<telerik:RadTreeView.ItemsPanel>
				<ItemsPanelTemplate>
					<telerik:TreeViewPanel ChildDefaultLength="48" />
				</ItemsPanelTemplate>
			</telerik:RadTreeView.ItemsPanel>
        <Style x:Key="ItemContainerStyle" TargetType="{x:Type telerik:RadTreeViewItem}">
			<Setter Property="ItemsPanel">
				<Setter.Value>
					<ItemsPanelTemplate>
						<telerik:TreeViewPanel ChildDefaultLength="48" />
					</ItemsPanelTemplate>
				</Setter.Value>
			</Setter>