For the time being you can use the following JavaScript workaround:
<html xmlns="http://www.w3.org/1999/xhtml">
<head id="Head1" runat="server">
<title></title>
<script src="//ajax.googleapis.com/ajax/libs/jquery/1.8.3/jquery.min.js"></script>
<script src="//ajax.googleapis.com/ajax/libs/jqueryui/1.10.4/jquery-ui.min.js"></script>
</head>
<body>
<form id="form1" runat="server">
<telerik:RadScriptManager ID="RadScriptManager1" runat="server">
</telerik:RadScriptManager>
<telerik:RadFormDecorator ID="RadFormDecorator1" runat="server" />
<script>
//Workaround:
var removeCssClass = Sys.UI.DomElement.removeCssClass;
Telerik.Web.UI.RadFormDecorator.prototype.set_elementDisabled = function (element, val) {
var actor = element;
var nextSibling = element.nextSibling;
var type = element.type;
if ((type == "checkbox" || type == "radio") && nextSibling && nextSibling.tagName == "LABEL") {
actor = nextSibling;
}
else if (type == "button" || type == "reset" || type == "submit" || element.tagName == "BUTTON") {
var parent = element.parentNode;
if (parent && parent.tagName == "A") {
actor = parent;
parent.disabled = val;
}
}
if (val) addCssClass(actor, "rfdInputDisabled");
else removeCssClass(actor, "rfdInputDisabled");
try {
if (!val && $telerik.isIE && actor.parentNode.disabled) {
actor.parentNode.disabled = val;
}
} catch (e) {
}
}
</script>
<input type="button" value="Test" onclick="Run(); return false;" />
<div id="TestDiv" style="display: none"></div>
<script type="text/javascript">
function Run() {
$('#TestDiv').dialog({
modal: true,
buttons: { "OK": function () { alert('bye'); } }
});
}
</script>
</form>
</body>
</html>