Unable to Backspace or Delete Characters In TextBox with FilteredTextBoxExtender

Unable to Backspace or Delete Characters In TextBox with FilteredTextBoxExtender in ASP.NET in opera browser. here is my sample code.

<asp:TextBox runat="server"  ID="TextBox1" MaxLength="20" />

                                    <asp:FilteredTextBoxExtender TargetControlID=" TextBox1 " ID="FilteredTextBoxExtender1"

                                        FilterType="Numbers,UppercaseLetters,LowercaseLetters" runat="server">

                                    </asp:FilteredTextBoxExtender>