I notice one weird behavior, on your sample it freezes the browser for a while and I can't continue working. It's a lot less time than my project but it freezes, do you face this issue? If so is there anyway to solve it?
I tried to handled copy by myself (using Telerik.Windows.Controls.Clipboard.SetText("Values");) but couldn't find a fast logic, if you have any I would be glad.
Another difference comparing to my project is that almost all columns are GridViewComboBox columns but on yours they are GridViewDataColumn, doesn't kown if this is part of the issue.
By the way do you think this freeze maybe memory related?