In one of my iParts, I'm using a Telerik RadGrid using the EditForms mode for editing a row.

<asp:Panel ID="body" runat="server" CssClass="PanelBody">
  <telerik:RadGrid ID="RADGrid" runat="server" CssClass="MultiDE" >
    <MasterTableView CssClass="Grid" EditMode="EditForms">
      <Columns>

When my grid includes a datetime field, this is rendered as a text input followed by an icon to open the DatePicker calendar.  At least, that's how it is on 15.1.2.

In 15.1.3 when browsing in IE8, the icon for the DatePicker is not displayed.  The space is still allocated on the page, and you still get the tooltip if you mouse over it.  If you click it, the calendar popup comes up, and you can interact with it, but you can see all the controls behind it.  It's pretty clear the problem is missing images, but the images come from WebResource.axd.

The same page displays correctly in Firefox 3.6.  Using the same code on iMIS 15.1.2.5454, the controls display correctly in both IE and Firefox.

How should I go about diagnosing a problem like this?  It looks like other WebResource.axd resources are being used correctly in both browsers.