Resizing the window containing a CartesianChart with SplineSeries leads to some incorrect rendering between points:

Inconsistency in Line and Spline series performance

creation of a line graph on a scatter point chart with gaps in the line when expected values are missing 

Something like this:

If we have a Chart with DateTimeContinuousAxis as horizontal axis, updating its Minimum and Maximum values should update the rendered in the Chart plot area data. However, if for some period (Minimum and Maximum range) there is no data, the current displayed data is not cleared.

If you populate the Chart with data through a SeriesDescriptor as explained here: How to Generate a Dynamic Series Using a Collection of Collections, the PointTemplate/PointTemplateSelector is not applied.

Currently the only way to apply different colors to the bars is through the ChartPalette. Provide an option to set the color according to the bound data item.  

updating data in real-time causes flickering when series are added through the series provider

Workaround: 
Add series to the chart without using the SeriesProvider option.

TelerikChartAxisBorderBrush is not applied when setting in Dark Light ThemeResources from the Telerik Theme Resources https://docs.telerik.com/devtools/universal-windows-platform/common/teleriknamedbrushes 

when applying the filter in a column where the scroll is on the right, all the scroll is reset to the left and the popup moves to another column. 

When the SelectionMode is set to Extended and we try to select items that are not currently visible using Shift + press only the Rows that are currently visible are selected.

Data can come dynamically from JSON, XML, and SQL.  Without the ability to bind a grid to commonly used structures (like a Newtonsoft JSON, .NET DataTable or Dictionary), this grid has VERY limited use for apps that use modern ways of gathering and managing data (like JSON-Schema).

When you are in tablet mode and try to type 6 from the on-screen keyboard - the "-" sign is applied. 

Provide a tabstrip control that allows users to display content on tabs.

 - Tab content could use virtualization to avoid extra rendering
 - Follow themes from Telerik
 

When the DataGrid is placed inside a Panel (for example Grid) and after that is removed from that panel and is placed in another one the selection stops working. The issue is caused by the inaccurate order of the thrown Unloaded and Loaded events which the control relies on.

When the RadNumericBox has focus it displays a clear button on the right, the "X".  In a high data density screen or grid, space can be at a premium and this button takes space, and when the user has a keyboard is not necessary (they can use the delete key) It would be space saving if this button was optional (as per the WPF version).

Universal combo box.

Add a setter for the AutoCompleteBox's SelectedItem property.

For example, to use different keys than the default arrow keys to switch from day -> month -> year in DatePicker