WPF Mouse Down Event won't fire

I must be doing something stupid here but I cant get a MouseDown event to fire when I am clicking on the UserControl. Driving me Mad. Here's the XAML for the UserControl: ``` <UserControl x:Name="cusTextBox" x:Class="StoryboardTool.CustomTextBox" xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation" xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml" xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006" xmlns:d="http://schemas.microsoft.com/expression/blend/2008" mc:Ignorable="d" d:DesignHeight="300" d:DesignWidth="300" MouseDown="cusTextBoxControl_MouseDown"> <Grid> <RichTextBox x:Name="richTextBox"> <RichTextBox.ContextMenu> <ContextMenu> <MenuItem x:Name="ContextMenuBringForward" Header="BringForward" Click="ContextMenuBringForward_Click"/> <MenuItem x:Name="ContextMenuSendBackward" Header="SendBackward" Click="ContextMenuSendBackward_Click"/> </ContextMenu> </RichTextBox.ContextMenu> </RichTextBox> </Grid> </UserControl> ``` Code Behind: ``` private void cusTextBoxControl_MouseDown(object sender, MouseButtonEventArgs e) { selected = (CustomTextBox)sender; } ``` Why wont this fire when I am clicking the User Control?