Thank you for your reports.
We are aware of this issue and it is logged in our bug-tracking system.
It is also logged in our PITS
application under the name "The TabItem doesn't changes when selected Item in the VS2010 designer
". You can track the progress and vote for this issue there.
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.