It happens in all browsers but I am using IE 9 specifically and you can use one of your online demos to reproduce the behavior which I assume is the latest release.
Steps to reproduce:
1,) go to the online demo at: http://demos.telerik.com/aspnet-ajax/combobox/examples/populatingwithdata/xmlstringbinding/defaultcs.aspx. This takes you to the XML String Binding demo.
2.) click on the Declarative Databases demo link on the left.
3.) Select on option from one of the combo boxes and hit the backspace key and it will return you to the XML Binding Demo page.
As long as there is a previous page in the browser history hitting the backspace will cause this behavior.