The problem is that when you have SearchMode=Contains , and have item that contains the entered text and one that starts with this text, the ComboBox selects the one which contains the text(as it is with smaller index) but scrolls to the one that starts with it.

When using similar code as below, RadComboBox does not select the specified item. If the DomainDataSource data was already loaded, the selection is successful.
<telerikInput:RadComboBox ItemsSource="{Binding ElementName=MineTypeDomainDataSource, Path=Data}"
  SelectedItem="{Binding Path=MineType, Mode=TwoWay, NotifyOnValidationError=true, ValidatesOnExceptions=true}"> 
 <telerikInput:RadComboBox.ItemTemplate> 
  <DataTemplate> 
   <TextBlock Text="{Binding MineTypeName}" HorizontalAlignment="Left" /> 
  </DataTemplate> 
 </telerikInput:RadComboBox.ItemTemplate>  
</telerikInput:RadComboBox>  
<riaControls:DomainDataSource AutoLoad="True"
  x:Name="MineTypeDomainDataSource"
  QueryName="GetMineTypesQuery"
  LoadedData="MineTypeDomainDataSource_LoadedData"
  DomainContext="{StaticResource CitationDBSvc}" />

The issue can be reproduced also with the standard ComboBox:
https://connect.microsoft.com/VisualStudio/feedback/details/663870/wpf-4-0-combobox-itemtemplate-and-selectionboxitemtemplate-when-itemtemplate-is-bound#details

If there are plenty items in RadComboBox and you double click an item to select it sometimes the wrong item is selected because of the animation.

RadComboBox and RadRibbonComboBox in their NonEditable mode do not reflect background set inline. A style for the ToggleButton contained in the NonEditable templates prevents the TemplateBinding from working properly as it uses a hard-coded background. For RadRibbonComboBox it is a Metro theme-only issue.

Properties like AutomationProperties.Name are not read if the RadComboBox is editable.

The combobox lists in Windows 10 settings (see attached pictures) have an interesting behavior which could be integrated by Telerik combox controls. The behavior is as following: when the listbox is opened, it appears above the combobox control with the selected item highlighted. And the placement of the listbox can change if the first item is selected (displayed down direction) or the last item is selected (display up direction).

It's difficult to explain that with simple words, so I suggest to see attached pictures to understand my request.