Compile issue

[derekantrican]

Not sure if this is related to #1 (because there's a huge lack of info) but I'm trying to compile in Avalonia 0.9.12 and getting the following build error:

Internal compiler error while transforming node XamlIl.Ast.XamlIlAstObjectNode:
XamlIl.XamlIlTypeSystemException: Content (or substitute) attribute is declared on multiple properties of Teast.Controls.GroupBox:Teast.Controls.GroupBox
at XamlIl.Transform.XamlIlTransformerConfiguration.FindContentProperty(IXamlIlType type)
at XamlIl.Transform.Transformers.XamlIlResolveContentPropertyTransformer.Transform(XamlIlAstTransformationContext context, IXamlIlAstNode node)
at XamlIl.Transform.XamlIlAstTransformationContext.Visitor.Visit(IXamlIlAstNode node) (line 16 position 6) Line 16, position 6. AvaloniaPropertyIssue C:\Users\derek\source\repos\AvaloniaTest\AvaloniaTest\MainWindow.axaml 16

I'm using the same code as the sample:

    <teast:GroupBox
        Header="This is a header">
      <StackPanel>
        <TextBlock Text="Sample text inside" />
        <Button Content="Sample button" />
      </StackPanel>
    </teast:GroupBox>