When DragElementAction="ExtendedSelect" in GridView is set, there is a problem with the deselecting
behaviour. Ctrl + click no longer deselects the row.

The problem should be resolved with lib version 2015.3.1019.

Columns data gets overlapped when columns are hidden and shown again

The header row (the group headers in a GridView, or a parent row in a TreeListView) stays in the screen while scrolling until all the children rows have been scrolled.

The feature is available in R3 2017 Release of UI for WPF.
Check what's new in R3 2017 here: 
http://www.telerik.com/support/whats-new/wpf/release-history/ui-for-wpf-r3-2017

1. Scroll to near the bottom of grid.
2. Refresh the Grid, populating it with less items.
3. Should see mostly blank grid besides for bottom row.
4. If you scroll any the rows show back up.

The grips on the scrollbar's thumb is blurred on 120dpi as well as some of the borders.

As it turns out, we hit a WPF specific problem with 120 DPI. The issue is similar to the following:
http://connect.microsoft.com/VisualStudio/feedback/details/798513/wpf-dpi-rendering-issues-with-two-borders
For the time being this issue is not addressed and most probably would not be fixed. 

Provide option to enable changing the column display index when dragging group cell into the header row.

Available in the 2017 R1 Release (2017.1.117).

Let your data column have a cell style with DataTrigger which sets the Tooltip depending on the value:

<telerik:GridViewDataColumn.CellStyle>
    <Style TargetType="telerik:GridViewCell">
        <Style.Triggers>
            <DataTrigger Binding="{Binding StadiumCapacity}" Value="42055">
                <Setter Property="ToolTip" Value="THIS IS TOO SMALL" />
                <Setter Property="Background" Value="Red" />
            </DataTrigger>
        </Style.Triggers>
    </Style>
</telerik:GridViewDataColumn.CellStyle>

Initially, when the grid loads - the tooltips are set correctly. But if you edit a cell and change its value to 42055 then the background is set to Red (as expected), but the tooltip does not update.

Add an ability for the user to select a full column (the SelectionUnit should be Cell and the SelectionMode should be Multiple or Extended). 

Consider this behavior in regard with the sorting of the column.

We would like to have the ability to merge cells vertically with same content. Consider to do the same horizontally.

Add Option to disable autoBring into View the focused RadGridView unit.

Currently, when a user selects multiple rows, but skips a few, and then copies, the data in the Clipboard will look as if the selected rows were in an uninterrupted sequence. Unselected columns, on the other hand, leave a "hole" in the clipboard data. This

There are two different styles for the Validation Message - the Microsoft's and the Telerik's.

When you place a DataTrigger whithin a CellTemplate, it is being ignored by RadGridView for WPF

Workaround ( until fixed ) - set the ContentTemplate of the cell via Style in a static resource instead.