to be honest i wasn't aware this was possible in the app. looks like it works like that if you have grouping enabled in the main UI.
i can add sorting by feed title using a separate option i guess, although this would break catchup above. i'm not gonna bother reworking the way it works so it simply won't be available in this configuration.
also you probably mean order by, not group by.
e: option should be added in next beta build (1.189)