The guy who wrote Yumiko's route isn't even a writer, he's a web designer, and it doesn't seem like he's going to be around for Frontwings new game starring the Grisaia cast.
Hm? About the riverside scene...
The way I see it is Yumiko at that time is really stubborn (even after the previous events) and Yuuji's there for the sake of following her orders. He's Yumiko's bodyguard after all so he can't do anything beside following her orders. Well, he can at least advise Yumiko but I doubt she'll listen to him unless something bad happen to her... or him.
Was I wrong? Just my opinion though
(Oh, and I like her dere side especially during 'Come Forth, Dere' scene in common route. She really loves compliments, wasn't she? )