ASP.NET button set enabled but page shows disabled

Question

I have a web page on which one can select a report and a printer to which to print, and then choose to print the report with a button. The button should be disabled until both a report and printer are selected. I use this to do so:

    Protected Sub PrintButtonUseability()
        btnPrint.Enabled = ddlPrinters.SelectedText.Length > 0 AndAlso rgWebReports.SelectedIndexes.Count > 0
    End Sub

Debugging indicates it is being set properly. But if I select something from ddlPrinters and then select something from rgWebReports, it turns out that, even though stepping through the code that btnPrint.Enabled is set to False, the button is disabled! Strangely, if I select from rgWebReports first and then select from ddlPrinters then it works as expected.

Additional information that seemed irrelevant was that I'm using a RadAjaxManager to clearly show the page is busy when retrieving data, especially when selecting a report.

Answer 1

It turns out, as I was about to post this question, I had a suspicion: maybe the delay somehow caused something to go haywire. Here is my RadAjaxManager:

    <telerik:RadAjaxManager ID="RadAjaxManager1" runat="server">
        <AjaxSettings>
            <telerik:AjaxSetting AjaxControlID="ddlPrinters">
                <UpdatedControls>
                    <telerik:AjaxUpdatedControl ControlID="pnlPrint" />
                    <telerik:AjaxUpdatedControl ControlID="btnPrint" />
                    <telerik:AjaxUpdatedControl ControlID="rgWebReports" />
                </UpdatedControls>
            </telerik:AjaxSetting>
        </AjaxSettings>
    </telerik:RadAjaxManager>

For some reason, removing the btnPrint and rgWebReports resolved my issue, and it works correctly. I am at a loss to explain exactly why it works, though.