Currently you should modify the template of the AutoCompleteBox in order show the scrollbar - I've attached an example showing the approach. Note that I'm using Implicit Styles
to style the control, so you should reference NoXaml assemblies. We will fix this for Q3 SP release.
As to the MinimumPopulateDelay
property - it will be implemented in some of the future versions of RadAutoCompleteBox.
We are sorry for the inconvenience, the help topic will be updated shortly.
the Telerik team