TextBox with CurrencyFormat and PropertyChanged trigger doesn't accept text right

Question

I have a TextBox in a WPF window bound to a dependency property of the window of type double (see below). Whenever the user types in the TextBox

Answer 1

This is caused by it trying to apply the formatting after every character press.

As an alternative, I usually just style the TextBox so it only applies formatting when it's not being edited

<Style TargetType="{x:Type TextBox}">
    <Setter Property="Text" Value="{Binding SomeValue, StringFormat=C}" />
    <Style.Triggers>
        <Trigger Property="IsKeyboardFocusWithin" Value="True">
            <Setter Property="Text" Value="{Binding SomeValue, UpdateSourceTrigger=PropertyChanged}" />
        </Trigger>
    </Style.Triggers>
</Style>