Change text on NotifyIcon Context Menu

[andrewwatson]

I've got a NotifyIcon with a context menu. I want one of the menu items to change its own text:

private void mnuItem_Click (object sender,System.EventArgs e)
{
    if (mnuItem.Text=="Do Something")
    {
        // Do something       
        mnuItem.Text="Do Something Else";
    }
    else
    {
        // Do something else
        mnuItem.Text="Do Something";
    }
}

When I select the menu item, it does what it's supposed to, but when I open the menu again, it's still displaying the old text. However, selecting the item again carries out the alternate action, as if the text had been changed!

Do I need to call something to notify the system that the menu's changed?