In v15.3.0.33, the WPF TreeViewAdv doesn't show any "root lines" when using one of the skins. If I add a TreeViewAdv to a window and set ShowRootLines="True" it'll show the lines just fine, but if I then enable a theme by adding skin:SfSkinManager.VisualStyle="Blend" to the ChromelessWindow or to the TreeViewAdv, the root lines don't appear.
So, for example, here's a simple TreeViewAdv with ShowRootLines="True" with a Red LineBrush:
If I then go and set the SfSkinManager.VisualStyle to Blend (or any other theme), the root lines are no longer visible:
The interesting thing is that some of the line does show up while the expand/collapse animation (I'm using "Slide" in this case) is playing, so it seems the lines are still in the ControlTemplate, they're just hidden, and for some reason, they become visible again while the Slide animation plays.