Will postback in asp.net always causes a "navigate away" warning
<p>I have a pretty simple questions that had stumped me so far ..
I am trying to do a one-level cascading drop down in ASP.NET.</p>

<p>So, I have two drop down boxes (among other text boxes), after ddlOne is selected, then ddlTwo will be populated.</p>

<p>here's my code in aspx</p>

<pre><code>&lt;asp:UpdatePanel ID="comboBoxWorkFlowPanel" runat="server"&gt;
&lt;ContentTemplate&gt;
        &lt;asp:DropDownList ID="ddlPendingUserGroup" runat="server" 
        DataTextField="groupName" DataValueField="groupId" OnSelectedIndexChanged="ddlPendingUserGroup_SelectedIndexChanged" AutoPostBack="true"&gt;                                                                                        
         &lt;/asp:DropDownList&gt;
        &lt;asp:DropDownList ID="ddlUserGroupUsers" runat="server" Enabled="false"DataTextField="userName" DataValueField="userID"&gt;&lt;/asp:DropDownList&gt;
&lt;/ContentTemplate&gt;
&lt;asp:UpdatePanel&gt;
</code></pre>

<p>and pretty much in the code behind page, 
the event handler will read from the drop down and then populate the second drop down.</p>

<p>my question is, after the selection is made in the first drop down,
why am i getting a warning message ("you're about to navigate away from this page")</p>

<p>If i click ok on the warning message, the dropdown box will be loaded correctly, and other values that were previously on the page will be preserved.
If i click cancel, i get a script error instead.</p>

<p>any thoughts on this?</p>

<p>thanks!</p>
