To reproduce: 
1. Enter some text and click the first button. Both properties, Text and Value contain the expected value.
2. Click the second button to clear the text and value.
3. Enter some text again and click the first button. You will notice that the Value remains empty. 

public RadForm1()
{
    InitializeComponent();

    this.radMaskedEditBox1.MaskType = Telerik.WinControls.UI.MaskType.None;
    this.radMaskedEditBox1.Mask = "CCCCCCC";
}

private void radButton1_Click(object sender, EventArgs e)
{
    this.radLabel1.Text = "Text: " + this.radMaskedEditBox1.Text;
    this.radLabel2.Text = "Value: " + this.radMaskedEditBox1.Value + "";
}

private void radButton2_Click(object sender, EventArgs e)
{
    this.radMaskedEditBox1.Clear();
}

Workaround: use MaskType.Standard