I'm trying to do some simple TextBox validation and found the ExceptionValidationRule class. My XAML is (basically)

Code:
<TextBox>
    <TextBox.Text>
        <Binding Path="MyText" UpdateSourceTrigger="PropertyChanged">
            <Binding.ValidationRules>
                <ExceptionValidationRule />
            </Binding.ValidationRules>
        </Binding>
    </TextBox.Text>
</TextBox>
and the MyText property is (basically)

Code:
public string MyText {
    get { return this.myText; }
    set {
        this.myText = value;
        if (!MyTextIsValid(value))
            throw new ApplicationException("Not valid.");
        else
            OnPropertyChanged("MyText"); } }
When run in debug mode, if I edit the text so that it becomes invalid, instead of just outlining the TextBox in red like I want, a debug window comes up saying the "Not valid." application exception was unhandled. When run outside of debug mode, it works properly.

I ran someone else's example code, though it wasn't written for VS2010. After running the upgrade wizard and the application, the same error appears. I also found a forum post which seems to describe my issue precisely, though it had no replies.

Since I've never used data validation before, I wanted to make sure I wasn't doing anything wrong and that this is indeed a bug. So, anybody have confirmation it's a bug or advice on what I'm doing wrong?


P.S. I'm aware there should be workarounds with the more complex validation techniques. I don't want to use them on principle, particularly since the non-debug version works fine.