Yeah, but the brothers didn't meet until well after Yoda knew something was up with Maul.
Okay, had a quick scan through it this morning. I don't have an issue with Yoda sensing it, as Maul was pretty much loopy this whole time, but then suddenly faced with his brother something seemed to half snap back into place in his brain. He suddenly seemed to remember some things, or at least suddenly had them thrown back in his face and that REALLY pissed him off. Strong, well trained and disciplined Sith suddenly with a brain full of nothing but revenge against someone Yoda knows well...yeah, I can let that one slide.
Overall, kind of a dissapointing episode though, and seems like a waste of one of the two remaining ones this season. It seems like not a whole hell of a lot happened, particularly as we all already knew who was in the shadows. Might have been different if it was in fact some kind of "HOLY SHIT!" surpirse rather than "Oh for fucks sake, get on with it and get him out here!" moment.