On excel, you can filter merged rows. On the kendo spreadsheet widget, filtering on merged rows is not possible. It would be a very useful feature for us. 

Also worth noting is that if you convert an excel file to JSON using Telerik RadSpreadProcessing, and load the kendo widget with the JSON, the widget displays a filter icon but clicking it loads a non-functioning filter. Wouldn't it make more sense to load with a message along the lines of 'You loaded a spreadsheet with filters applied to merged rows, which is not supported in this widget'. Otherwise it's quite confusing to our users.