Values disappears on the textBox

Question

The below is the code,

 

When I tab out after entering the values in the text box(txtCVV)they disappears and when i right click and undo I and able to retrieve the values

 

Similarly, when i click on the textBox, the values disappears and when i right click and undo I and able to retrieve the values

 

Can someone help me resolve this.

 

<div class="column tiny-12 small-6 medium-5" data-securityzipcode-content>

<label class="margin-right-tiny" id="Label2">

<span class="text-brand-1">* </span>Security Code:</label>

<asp:TextBox ID="txtCVV" TextMode="Password" MaxLength="4" data-id="number"

CssClass="w-tiny DisableCopyPaste" onPaste="event.returnValue=false;return false;"

ondrop="return false" ondragstart="return false" onselectstart="return false"

autocomplete="off" runat="server" ClientIDMode="Static" Style="display: inline;

width: 150px;">

</asp:TextBox>

<input type="hidden" id="hdnCVVWallet" runat="server" clientidmode="Static" />

</div>