WPF: Bindings not working correctly - wpf

Question

Say I have XAML like
<TabControl Grid.Row="1" Grid.Column="2" ItemsSource="{Binding Tabs}" IsSynchronizedWithCurrentItem="True">
<TabControl.ItemTemplate>
<DataTemplate>
<TextBlock Text="{Binding TabTitle}" />
</DataTemplate>
</TabControl.ItemTemplate>
<TabControl.ContentTemplate>
<DataTemplate>
<local:UserControl1 Text="{Binding Text}" />
</DataTemplate>
</TabControl.ContentTemplate>
</TabControl>
I want to ask where does the TabTitle and Text properties come from? I think the should come from each item of Tabs right? Say Tabs is a ObservableCollection<TabViewModel> TabTitle & Text should be from TabViewModel properties right. But it seems true to a certain extend. TabTitle is populated correctly while Text is not.
Text is declared as a Dependency Property in UserControl1 as follows
public string Text
{
get { return (string)GetValue(TextProperty); }
set { SetValue(TextProperty, value); }
}
public static readonly DependencyProperty TextProperty =
DependencyProperty.Register("Text", typeof(string), typeof(UserControl1), new UIPropertyMetadata(""));
When I have tabs not bound to a ObservableCollection<TabViewModel> bindings works fine
<TabControl Grid.Row="1" Grid.Column="1">
<TabItem Header="Tab 1">
<local:UserControl1 Text="Hello" />
</TabItem>
<TabItem Header="Tab 2">
<local:UserControl1 Text="World" />
</TabItem>
</TabControl>

Answer 1

If you are binging UserControl to the property from code-behind file, you should use
{Binding RelativeSource={RelativeSource Mode=Self}, Path=Text}
Direct binding as u have works only for DataContext

Answer 2

I think I know what is the problem. The element in the UserControl1, which should be filled by Text property, doesn't observe the changes of this property. So there is two ways:
1) Use PropertyChangedCallback:
public static readonly DependencyProperty TextProperty =
DependencyProperty.Register("Text", typeof(string), typeof(UserControl1), new UIPropertyMetadata(""),
new PropertyChangedCallback(OnTextPropertyChanged));
private static void OnTextPropertyChanged(DependencyObject sender, DependencyPropertyChangedEventArgs e)
{
((UserControl1)sender).OnTextChanged();
}
private void OnTextChanged()
{
this.myTextBlock.Text = this.Text;
}
2)Tricky binding:
<UserControl x:Class="UserControl1" x:Name="root" ...>
...
<TextBlock Text="{Binding Text, ElementName=root}"/>
...
</UserControl>