I built up a test page based on your code and with the 2009.1. 402 version of radcontrols as you have noted. After that I tested under IE8, IE7 and FF because you did not provide information about the browser but unfortunately to no avail - the RadSlidingPanes were expanding as expected - please see the attached video capture for a reference of the result on my side.
The only thing I can assume that might be causeing the issu eis that you have missed teh fact that you have set the ClickToOpen property to true and you want to expand the sliding panes on hover - if so, please remove the setting or click on teh tab to expand teh pane. More information about the ClickToOpen property is available below:
In case this is not the problem, please examine my video capture and let me know what I am doing wrong or try to reproduce the issue in our online demos. Provide also some information about the brpwser under which teh problem occurs.
All the best,
the Telerik team