title: NumericUpDown UpdateEditText causing problems when entering values
body: <p>I've created a very simple NumericUpDownPlus which overrides the UpdateEditText method in the following way: (As per this SO question: <a href="https://stackoverflow.com/questions/5921446/having-text-inside-numericupdown-control-after-the-number">Having text inside NumericUpDown control, after the number</a>)</p>
  
  <pre><code>protected override void UpdateEditText()
  {
      if (string.IsNullOrWhiteSpace(Units))
      {
          base.UpdateEditText();
      }
      else
      {
          this.Text = this.Value + " " + Units;
      }
  }
  </code></pre>
  
  <p>However, this causes me problems when editing the control manually. In this case, I'm appending " px" as my Units, and the following situations can arise:</p>
  
  <ol>
  <li>I select the entire value, including px and write in another, i.e., 400 and it works, and re-appends the px.</li>
  <li>I select only the number value, leaving px, and enter a new value, however it thinks px is part of the new value, and reverts to the old value straight away.</li>
  </ol>
  
  <p>Of course, I'm only interested in the number, and don't care what unit is being used, it's just a convenience for the user. How can I get this NumericUpDown to cooperate? I was thinking of just clearing the box when control gets focus, but I feel like this might not be the best solution.</p>