The issue can be reproduced in a scenario in which there are a RadListBox and a RadGridView defined and their SelectedItem properties are bound to the same property in the view model. The source collection of RadListBox contains some objects present in the one bound to RadGridView's ItemsSource. If the user selects an item in RadGridView that is also present in the items of RadListBox, the selection is performed in both controls as expected. However, when already having a selected item in both controls, if the user selects an item in RadGridView that is not present in the items of RadListBox, the selection in RadListBox is not cleared. Thus, in order to selected the previously selected item, it needs to be deselected and selected again.

UPDATE:
After the researching the issue, it seems that the logic for handling the case when a SelectedItem that is not present in the source collection is being set is slightly different for Silverlight and WPF. For the WPF version of the control a DependencyProperty.UnsetValue is used, whereas a null value is set for the Silverlight RadListBox. Thus, in Silverlight the selection is cleared and in WPF it is not. I am afraid, that we cannot commit ourselves to modifying this by-design implementation, as this will result in a braking change. With this in mind, I will update the status of the logged bug to Declined.

What we can suggest as a workaround, would be to define a second calculated property in the view model and bind the SelectedItem of RadListBox to it. The logic in the property setter would be to set a null value if the SelectedItem is not present in the source collection of RadListBox.

When the ItemsPanel of the RadListBox is RadWrapPanel and the user press Down/Up key the RadListBox selects always the next/previous item instead of the corresponding item on the next/previous row.

Available in LIB version 2018.1.205, it will be also available in the R1 2018 SP2 Release.

As a workaround, the ScrollingSettingsBehavior.ScrollStep attached property of the RadListBox control can be set to a value equal to that of the Height of the RadListBoxItems.

Available in R3 2017 Official Release Version.

Available in R3 2017 Official Release Version.

Available in the R1 2017 SP1 Release.

A workaround is to use the SelectedItem of the control and get the value of the needed property of the item.

Available with the R3 2016 SP1 release. 

Available in LIB version 2016.3.1017, it will be also available in the 2016 R3 SP1 release. 

When the ItemsPanel is set to VirtualizingStackPanel which Orientation is set to Horizontal, selecting an item moves it to the rightmost position.

Available in LIB version 2016.3.1017, it will be also available in the 2016 R3 SP1 release. 

RadListBoxItems looks selected when BusyIndicator is made busy

ListBoxItem is going to the last position when dragged and dropped in to the SCrollViewer.

ListBoxItem disappears when the item is dropped in the RadGridView

This happens when using VirtualQueryableCollectionView as the ItemsSource.

I have a custom ListBox that inherits from RadListBox control which uses a VirtualizingWrapPanel as its ItemTemplate.
I am trying to use BringIndexIntoViewPublic method to bring a certain ítem that is still not created into view, but it does not work. I also try to use ScrollIntoView of the RadListBox, and is also not working.

Scroll button is changing size when grouping is applied (WPF only).

When RadListBox is in a ScrollViewer and its own ScrollViewer is removed, it uses the external ScrollViewer for calculating DropVisualPlaceHolder position.