Indeed we must admit there was a problem with handling big numbers in the latest official version of the control.
However, our developers have already managed to address the issue so you can download the weekly internal build from your Client.Net account to get the fixed version (the fix will also be included in the official service pack release scheduled for later this week).
Hope this helps.
the Telerik team
Do you want to have your say when we set our development plans?
Do you want to know when a feature you care about is added or when a bug fixed?
Telerik Public Issue Tracking
system and vote to affect the priority of the items