Thank you for contacting us.
In the current version of RadAutoCompleteBox you can access the typed text from the SearchText property and the auto completed text from the SelectedItem property of the control.
There is an existing issue concerning the SearchText property of the control that we are aware of which is causing the need to access the auto completed text from the SelectedItem property. We logged it in our Public Issue Tracker System
where you can vote for it and track its status.
We will do our best to have a permanent fix for it in our next official Q1 2013 release of RadControls.
We apologize for any inconvenience that this may be causing.
the Telerik team