Created Issue: ToggleButtonExtender not rendering images [27359]

I am using AjaxControlToolkit 4.5.7.123 with a Target framework of .NET Framework 4.5. The page contains the ToolkitScriptManager control. There are user controls on the page, each of which contains controls similar to the following:

<asp:CheckBox ID="Compensation_Cbx" runat="server" Checked="false" AutoPostBack="true" />
<act:ToggleButtonExtender ID="Compensation_Toggle" runat="server" TargetControlID="Compensation_Cbx" ImageWidth="20" ImageHeight="20" CheckedImageUrl="/Images/Buttons/Minus.gif" CheckedImageAlternateText="Hide compensation." UncheckedImageUrl="/Images/Buttons/Plus.gif" UncheckedImageAlternateText="View compensation." />

The images do not render over the checkbox at all. I have verified that the images are on the server in the correct locations. I have also tried using the full URLs of the images, but that made no difference.