GridViewDataColumn.IsVisible binding is broken in a custom scenario. The problem is reproducible only in child GridView.

It should be resolved with lib version 2015.1.504.

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.

The issue is reproducible with Q1 2015 SP1 version. With Q1 2015 it is not.
In order to reproduce it, add at least one empty cell. When you try opening the excel file you get the an error that Excel will try to recover the file.

Should be resolved with LIB version 2015.1.413.

 Introducing an overload of ExportAsync that exposes some "export finished callback" that could be a custom Action delegate. 

When RadGridView is grouped by a column with ShowColumnWhenGrouped property set to False and GroupDescriptors are cleared, the column does not get visible. 

The sort index will not be displayed when applying a custom sorting without adding a SortDescriptor, You can consider implementing Custom Sorting using the IComparable interface instead. As an example please refer to the Custom Sorting with IComparable WPF Demo. Using a generic SortDescriptor would also be an option. 
Please check our online documentation for a further reference: http://docs.telerik.com/devtools/wpf/controls/radgridview/sorting/custom