TextBox: Should IsTextPredictionEnabled disable 'suggestions' popups?

[grork]

When working with TextBox, I've set IsTextPredictionEnabled to false, and expected it to prevent this popup from showing. However, as per the screenshot attached, it doesn't seem to. Of note, this particular textbook has its InputScope set to EmailSmtpAddress as well -- which I would have expected to suppress this suggestion popup as well.

Full markup:

<TextBox PlaceholderText="Your username..."
                 Text="{x:Bind ViewModel.Email, Mode=TwoWay, UpdateSourceTrigger=PropertyChanged}"
                 InputScope="EmailSmtpAddress"
                 IsSpellCheckEnabled="False"
                 IsTextPredictionEnabled="False" />