The panel allocates empty space for items that are hidden by setting their Visibility to Collapsed. Such items should be ignored when the panel arranges its items.

To work this around, instead of the Visibility property, you can remove and add the items in the ItemSource collection whenever you need to toggle their visibility.

Tab selection does not work in the VS designer when switching between different views.

If you define two UserControls in a project and you add two RadTabControls - one RadTabControl per UserControl, then in design-time you can only change the selection of one of the tab components.

Setting transparent background to RadBookItem doesn't work properly.

When an application is built with .net version 4.7, the paragraph dialog is clipped in the bottom.

 Group rows which are not present in the view are not visualized when the window is maximized.

A possible solution here is to set the GroupRenderMode property to Flat.

When there are items with longer text than the FilteringControl's default width, the FilteringControl resizes when scrolling to these items. This behavior is observed with all themes, different from Windows 8 and Windows 8 Touch.

"Win32Exception (0x80004005): Not enough storage is available to process this command" is thrown when multiple RadDocument instances are created in background threads. 

This is due to the fact that RadDocument contains MailMergeDataSource object, which is DependencyObject. When multiple dependency objects are created in different threads, they are not property freed by thread's Dispatcher.

Workaround 1: Microsoft provided workaround in a bug report here:
https://connect.microsoft.com/VisualStudio/feedback/details/620588/system-componentmodel-win32exception-0x80004005-not-enough-storage-is-available-to-process-this-command , namely:
------------------------------
Put the following code:

Dispatcher dispatcher = Dispatcher.CurrentDispatcher;
dispatcher.BeginInvokeShutdown(DispatcherPriority.Normal);
Dispatcher.Run();

anywhere in the background thread processing the RadDocument.
-----------------------------

Workaround 2: Use pooling of the used threads. The problem is that Task Parallel Library (which has built-in pooling) does not use STA threads by default, but this can be achieved by using custom TaskScheduler (attached, the code is get from here: https://code.msdn.microsoft.com/ParExtSamples ):

            var parallelOptions = new ParallelOptions()
            {
                TaskScheduler = new StaTaskScheduler(Environment.ProcessorCount)
            };

            Parallel.For(0, 10000, parallelOptions, cc =>
            {
                    var document = new DocxFormatProvider().Import(data);
                    byte[] pdfBytes = new PdfFormatProvider().Export(document);

            };

Exporting documents that contain PNG images SMask and ImagesDeflaterCompressionLevel is set to a non-default value may produce a document in which those images are not processed correctly by Adobe reader.

On export to HTML tab stops are converted to non-breaking spaces ( ). Sometimes the width of the all nbsp-s becomes different than the width of the tab stop. When document which contains grid-like data is exported to HTML its columns are not aligned.

The content of the cell is set from .LoadContent() method and is returned from the CreateCellElement method of the column. 

One possible scenario for a fix is to change that behavior and apply directly the template as WPF DataGrid does. However, this is a huge breaking change with CreateCellElement method is widely used. The second approach is to leave the code as it is right now, return the element from method of DataTemplate and set the ContentTemplate property of the cell to that DataTemplate. This will cause the content to be loaded twice. Which will degrade the  

So, as it turns out the solution is either to introduce breaking change or degrade the performance. Both of them are against our believes and efforts to improve the controls. 

Our suggestion is to use a workaround -  setting triggers directly to the style. We do hope you understand our concerns. 

The fix for this issue will be available with the next LIB (version 2018.3.1224) expected on Monday, December 24.

This behavior is reproducible when we have applied Material theme and we have disabled the selection and drag of a RadTreeViewItem. 
A possible workaround is to set the MaterialAssist.CheckedBrush attached property to Null of the RadTreeViewItem which you don't want to select and drag.

 xmlns:material="clr-namespace:Telerik.Windows.Controls.MaterialControls;assembly=Telerik.Windows.Controls"

 <telerik:RadTreeViewItem Header="RootItem" material:MaterialAssist.CheckedBrush="{x:Null}" />

The Expression property of the PropertyNameMetadata is used as a base for a Regex that is run against the property names of the object that is being serialized. Therefore, you should consider it a regex expression and set its value as in the following example:
- to match only the property "Width" - use the expression "^\b(Width)\b$", without the quotes.
- to match the "Width", "MinWidth" and "MaxWidth" - use the expression "Width", without the quotes.

Multiple operations applied on a big RadBitmap can cause OutOfMemoryException because of used and not disposed unmanaged resources in a WriteableBitmap object.

Steps to reproduce:
- Execute multiple times the Rotate tool
Observe: The memory goes up and retains such.
Expected: The unmanaged memory is cleared.

Findings: the memory leak is related to the WPF class WriteableBitmap which is internally used by the RadBitmap. Attached is a sample project illustrating the problem using only WPF classes.
Note: At this point, we are not aware of a possible fix.

When using an ItemContainerStyle on the second(non-root) BarItems, the Background doesn`t apply

When the properties are bound in code behind, they are not updated as they are supposed to.

Binding them in XAML, by setting the DataContext of the control as StaticResource, works as expected.