I can see the whole continuity thing you're going for with Yoda, but I find it infinitely cooler that R2 is the only one who knows what's going on the whole time. That, and the scene in question where Bail tells Antillles to erase C-3PO's memory (with R2 laughing) is classic Star Wars humor. And what is the big deal with R2 fighting Yoda anyway? Regardless if he knew who he was not not, he was stealing Luke's property and R2 wasn't going to stand for it. That's how I see it anyway.