Commented Issue: [AvalonDock 2.1] Unable to dynamically properly add tools [20833]

Referring to AvalonDock 2.1 (Commit 106497), I setup a simple window with a DockManager.
```

<xcad:DockingManager
AnchorablesSource="{Binding Path=Tools}"
>
<xcad:DockingManager.Theme>
<xcad:AeroTheme />
</xcad:DockingManager.Theme>
<xcad:DockingManager.LayoutUpdateStrategy>
<local:LayoutInitializer />
</xcad:DockingManager.LayoutUpdateStrategy>
<xcad:LayoutRoot>
<xcad:LayoutPanel Orientation="Vertical">
<xcad:LayoutPanel Orientation="Horizontal">
<xcad:LayoutDocumentPane />
</xcad:LayoutPanel>
</xcad:LayoutPanel>
</xcad:LayoutRoot>
</xcad:DockingManager>
```

The goal is to be able to dynamicall add anchorable tools at run time, in the proper location.
The AnchorablesSource property is bound to an observable collection of ITool. ITool exposes a property specifying the preferred location for the tool. The LayoutInitializer attempts to position the tool in the proper pane when it is loaded.

In the attached example, the Window's Onloaded event simulates an user that attempts to load a couple of tools. My current implementation correctly behaves when a left tool is loaded before a bottom tool. Instead, it fails if the bottom tool is loaded first.

Any suggestion/bug fix/workaround would be appreciated.
Comments: ** Comment from web user: Xceed **

"On that note, I'm not a big fan of the way the Community edition lags behind the commercial edition by one release. That's fine for new features - you guys have to make money somehow - but it really sucks when waiting for bug fixes like this one."

Noted. We'll think about how that could be made better (meaning, decide if we agree, and also how we would go about delivering bug fixes but not new features. We used to do it through a license key system with our other products, not anymore though).