Element visibility tied to radiobutton group selection causes the group to freeze - wpf

Question

I have a data bound RadioButton group in which one RadioButton (Replace) controls the visibility of another element.
When I select the Replace button the group becomes unresponsive. Interestingly, so does the form Cancel button. However, the OK button, which is implemented as a command continues to function (The Cancel button is just implemented as IsCancel="true").
<Border x:Name="pnlOptions" Margin="10" Background="AliceBlue" BorderThickness="2" CornerRadius="25">
<GroupBox TextElement.FontSize="14" TextElement.FontWeight="Bold" >
<StackPanel Orientation="Vertical">
<RadioButton GroupName="grpOptions" Margin="10,10,0,0" IsChecked="{Binding Path=SegmentSplitOption, Converter={StaticResource EnumRadioButtonConverter}, ConverterParameter={x:Static model:eSegmentSplitOption.Replace},Mode=TwoWay}">Replace original segment.</local:RadioButton>
<RadioButton GroupName="grpOptions" Margin="10,10,0,0" IsChecked="{Binding Path=SegmentSplitOption, Converter={StaticResource EnumRadioButtonConverter}, ConverterParameter={x:Static model:eSegmentSplitOption.Start},Mode=TwoWay}">Place at Start.</local:RadioButton>
<RadioButton GroupName="grpOptions" Margin="10,10,0,0" IsChecked="{Binding Path=SegmentSplitOption, Converter={StaticResource EnumRadioButtonConverter}, ConverterParameter={x:Static model:eSegmentSplitOption.Finish},Mode=TwoWay}">Place at End.</local:RadioButton>
<RadioButton GroupName="grpOptions" Margin="10,10,0,10" IsChecked="{Binding Path=SegmentSplitOption, Converter={StaticResource EnumRadioButtonConverter}, ConverterParameter={x:Static model:eSegmentSplitOption.Mid},Mode=TwoWay}">Place at Drop Location.</local:RadioButton>
</StackPanel>
</GroupBox>
</Border>
<StackPanel Grid.Row="2" Grid.Column="0" Grid.ColumnSpan="3" Orientation="Horizontal" Visibility="{Binding DurationVisibility}">
<Label>Duration</Label>
<local:TextBox Grid.Row="2" Grid.Column="1" x:Name="txtDuration" Width="80" HorizontalAlignment="Left" VerticalAlignment="Bottom" FontSize="14"
Text="{Binding Path=DurationMinutes, Converter={StaticResource DecimalHoursConverter}, Mode=TwoWay}" Style="{StaticResource GeneralTextBoxStyle}"/>
<Label Grid.Row="2" Grid.Column="2">(hh.dd)</Label>
</StackPanel>
private eSegmentSplitOption _SegmentSplitOption;
public eSegmentSplitOption SegmentSplitOption
{
get { return _SegmentSplitOption; }
set
{
if (_SegmentSplitOption != value)
{
_SegmentSplitOption = value;
NotifyPropertyChanged("SegmentSplitOption");
NotifyPropertyChanged("DurationVisibility");
}
}
}
public Visibility DurationVisibility
{
get { return _SegmentSplitOption == eSegmentSplitOption.Replace || _SegmentSplitOption == eSegmentSplitOption.NotSet ? Visibility.Collapsed : Visibility.Visible; }
}

Answer 1

The problem lay elsewhere in the CmdOK_CanExecute function which had the following code:
e.CanExecute = _SegmentSplitOption == eSegmentSplitOption.Replace || _DurationMinutes.HasValue && _DurationMinutes.Value > 0;
if (wPrevCanExecute != e.CanExecute && e.CanExecute)
{
Application.Current.Dispatcher.Invoke(new Action(() =>
{
btnOK.Focus();
}));
}
The intent was to set focus to the OK button when the command became able to execute. Why this should lock the radio buttons and the Cancel button is still a mystery.