Hello Iurie Coroban,
We must admit this is a bug within the control when the pie contains a single item.
Unfortunately we cannot suggest you a workaround at the moment but we will do our best to resolve this problem by the end of the week so the fix will be included in the weekly public internal build scheduled for Friday (you will be able to download the fixed version from your Client.Net account).
We have updated your telerik points for the report as well.
the Telerik team