Esses and me work on same project so I elaborate our xaml hierarchy a bit.
We have "MainEditor.xaml" which contains
All of those tabitems are our own usercontrols which looks something like this
Here you can see element "Viewport" which is present on all of our individual editors.
Viewport is just
<Grid x:Name="Viewport" Background="Transparent" />
This viewport is just what Unity is rendering. In our case, just making viewport's prop IsHitTestVisible to false will not fix our issue because there is always some element which catches viewport click.
I'm wondering if we are doing something wrong because if you use Noesis in Unity there is always some "root" element present which is obviously always catching Unity's mouse click events so obviously there is something wrong with our project...?
Here is image of the actual ability editor where you can see how the viewport looks
After investigating a bit this it looks like TabControl from MainEditor is somehow capturing click event.
I'm quite sure this is a bug, if your customer wants to use TabControl in Unity while still being able to click on unity objects, it's not possible at this moment
Repro: Open your primitives sample scene, open primitives.xaml
Group Grid named "layoutroot" to TabControl and make TabControls background transparent and make "layoutroot" as TabItem of this TabControl. Obviously you can't anymore click on primitive objects because this TabControl is consuming clicks.