It hasn't been unknown to see the circlips assembled backward: Gammaflat's 750K5 slipped a gear over this issue because the flat side of the circlip was up against the (adjacent) spinning thrust washer, and it eventually unseated the clip. Then, whenever he was in 2nd gear and leaned the bike over, it would make a loud clunking noise.
So, look thru your setup, and discover if the part(s) resting against the clip are rotating against it (or the thrust washer that is next to it). If so, the rounded side of the clip (or washer) goes against the part that is moving. If the adjacent part is cogged to the shaft and not turning, it is not necessary for the rounded side to be up against it: then it's a tossup. Both situations exist in this tranny, too!