I have a slider which binds to a property with slow getter and setter. Since the UI needs to be responsive, the binding has the attribute `IsAsync`. But when I drag the slider it jumps between the cursor and 0 (default `FallbackValue`).

Does anybody know how to prevent this behavior, how to disable the `FallbackValue`?

XAML:

```
<Slider>
  <Slider.Value>
    <Binding Path="Value" IsAsync="True"/>
    <!-- For testing, best plan till now
    <PriorityBinding>
      <Binding Path="Value" IsAsync="True"/>
      <Binding Path="CurrentValue"/>
    </PriorityBinding>
    -->
  </Slider.Value>
</Slider>

```

Code Behind:

```
public int Value
{
  get
  {
    //if (setterCount > 0)    // For testing, best plan till now
    //{
    //  return CurrentValue;
    //}
    Thread.Sleep(100);        // Just for simulating slow functionality
    return myValue;
  }
  set
  {
    //++setterCount;          // For testing, best plan till now
    //CurrentValue = value;
    Thread.Sleep(200);        // Just for simulating slow functionality
    myValue = value;
    //--setterCount;
    OnPropertyChanged("Value");
  }
}

```