Commented Unassigned: SliderExtender not working since upgrade [27936]

The following markup previously worked without issue before I upgraded to the devexpress managed version of the toolkit (v15.1.2 and recently v15.1.3)

<asp:TextBox runat="server" ID="txtSlider"></asp:TextBox>
<asp:TextBox runat="server" ID="txtSliderValue"></asp:TextBox> %
<asp:SliderExtender runat="server" ID="sliderExtender"
TargetControlID="txtSlider" BoundControlID="txtSliderValue"
Minimum="0" Maximum="100" Steps="100"/>

Since the upgrade, I now get the following java script error thrown and the slider doesn't render

__Error: Unable to get property 'Slider.Handle-Horizontal.gif' of undefined or null reference__

The error is thrown in ScriptResource.axd line 117

var defaultHandleImageUrl = (this._isHorizontal)
? Sys.Extended.UI.Images["Slider.Handle-Horizontal.gif"]
: Sys.Extended.UI.Images["Slider.Handle-Vertical.gif"];

Sys.Extended.UI exists but Sys.Extended.UI.Images is undefined

What has changed that has broken this int he new versions?
Comments: Since v15.1, SliderExtender renders slider images inside the OnPreRender method. This behavior caused the error you described. Now, the issue is fixed and will be available in one of our future releases.