I created a document type and matching template. i deleted the document type and recreated it (i did not remove the first template) with matching template. I ended up with two templates with the same name. i try to delete one (either results in same error) and get the following (via firebug):

{"Message":"Item has already been added. Key in dictionary: \u0027news article\u0027 Key being added: \u0027news article\u0027","StackTrace":" at System.Collections.Hashtable.Insert(Object key, Object nvalue, Boolean add)\r\n at System.Collections.Hashtable.Add(Object key, Object value)\r\n at umbraco.cms.businesslogic.template.Template.initTemplateAliases()\r\n at umbraco.cms.businesslogic.template.Template.delete()\r\n at umbraco.templateTasks.Delete()\r\n at umbraco.presentation.create.dialogHandler_temp.Delete(String NodeType, Int32 NodeId, String Text)\r\n at umbraco.presentation.webservices.legacyAjaxCalls.Delete(String nodeId, String alias, String nodeType)","ExceptionType":"System.ArgumentException"}