When the CheckBox is focused the issue is appearing. Available in LIB version 2016.2.905, it will be also available in the 2016 R3 Release.
Workaround: use OnDropDownClosed event.
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.
The same issue can be observe when placing the control inside ToolBar.
Enable the ComboBox to open its DropDown in up as well as down direction
When you click on the TextBox of an editable RadComboBox all the text should be selected, but it is not, even when SelectAllTextEvent="All" is set. The text is blinking as selected for half a second and then deselects.
When filtering is enabled, enter text that doesn't exist in the items and when the focus is removed the text entered is deleted, but it should stay. The solution of this issue was implemented by a new feature in the control which determines if the Text of the RadComboBox should be updated on LostFocus or not. Simply set the UpdateTextOnLostFocus dependency property of the control to "False". By default its value is True and no change in behavior should be observed. The UpdateTextOnLostFocus dependency property is available in the 2015 Q2 SP1 release.
Place a RadComboBox control in a RadPane. Make it floating and dock it again. When selection is changed, the SelectionChanged event is fired multiple times.
After RadComboBoxs DropDown (PopUp) is open moving the focus with Shift+Tab skips the Combo, Tab does not skip it Available in R2 2015 Release (v.2015.2.623.40)
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.
IsEditable=True and ReadOnly=True
Properties like AutomationProperties.Name are not read if the RadComboBox is editable.
Specifically this bug was found in WPF, I'm not sure of its state in Silverlight. The FontWeight is permanently some shade of Bold when using Metro. This is demonstrated in the Telerik WPF demos in the ComboBox/Theming demo.
This would provide the option to stop the auto scrolling when the last item is hovered.