Thanks for the feedback. We are aware of this issue - it is also valid for the search-by-letter functionality.
In queries against an Active Directory data source the wildcard ( * ) is equal to the wildcard ( % ) in sql syntax.
For example, if you search for "john
with an sql provider your query is similar to: SELECT ... WHERE username LIKE %john%
... and if you use an active directory provider your query should be similar to: ... (sAMAccountName=*john*) ...
This bug is already fixed the changes will be available with the service pack.
the Telerik team