I THINK this might actually have to do with the expansion animation, maybe?

Yes, you are right, the problem is the expand animation. I have to check it but I guess this kind of style will fail to bring the item into view also in WPF.
Anyway, our theme provides a non-animated TreeViewItem style too:

<Style TargetType="TreeViewItem" BasedOn="{StaticResource {x:Type TreeViewItem}}">

<Setter Property="Template" Value="{StaticResource Template.TreeViewItem.NoAnim}"/>

</Style>

I found some other Themes to be working as well. Maybe they have a shorter animation.
Yes I'd assume this fails in WPF too. I've had the problem of animations causing issues in this regards in other projects too. I guess it's a problem that can't really be resolved nicely.