The described problem was a bug which we recently found in the RadSlider control. However, it was fixed and the fix is already available in our latest release, namely Q3 2008 Beta, version 2008.2 1016 - if you upgrade to it, the problem should disappear. I recommend to wait until our next Q3 2008 release is available which is scheduled for this week and upgrade directly to it.
the Telerik team
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