If I don't have a summaryfeature I am not able to edit summaryType and summaryRenderer even if I have a groupingsummary feature.
Also, the summaryfeature appears after the groupingfeature if I have both in the grid, but If I only have the groupingfeature (with no grouping) I don't have a total summary row.
I have modified the CarListings example from Sencha to include the groupingfeature and show that is not working correctly. Maybe I am doing something wrong. It seems like the order for the features is important.
The code is attached.
Moreover, I have made a video that can be open using Firefox (or VLC) to show that is not working properly: