It should be resolved with lib version 2015.1.504.

When Unicode characters are copy pasted from grids via CTRL + C and then pasted into Excel or Word (for example) as a HTML table, it seems like for every Unicode character a certain amount of bytes / characters are cut off from the end result.

StackOverFlowException when the GroupMemberPath is set to a different path to the data member and the column is grouped, and filtered.

As an example I add a column to the grid:
columns.Add(new GridViewDataColumn() { DataMemberBinding = new Binding("CustomerId"), GroupMemberPath = "CustomerName", SortMemberPath="CustomerName", Width = 300 });

When the grid appears, drag the CustomerId column to the grouping area
Click the filter icon on the CustomerId column
Click a checkbox in the filtering control to select an item
Exception occurs

The problem should be resolved with lib version 2016.1.125.

When dealing with Date column filters show available options (similar to text filters) and support grouping based on Year, Month. This is a very handy feature of Excel.

Workaround:

Define an implicit Style targeting GridViewRow UI element under Window.Resources or RadGridView.Resources section.

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.

* Workaround: commit the edit before removing the item
* Works fine with the old Nested mode

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