Due to this behavior the font name applied is getting cleared when switching to HTML mode.
The issue is fixed with the current version of Telerik UI for ASP.NET. You could test the scenario here: http://demos.telerik.com/aspnet-ajax/editor/examples/overview/defaultCS.aspx
This item is added to the queue and it is up to further planning to be added into the to-do-list for further investigation by the developer team. Any further updates on the task will be posted here.
Any news here?