Hmmm, I haven't had problems with any of my itti bittis, they're my faves because they never leak lol. That said though, I didn't use the tuttos on DD when she was small because the fit just wasn't right, even on the smallest setting.

With my other nappies, when they do leak it's usually because they've been on too long and I haven't been able to change her for whatever reason, or because DH does up the snaps funny lol. So as Rowellen says, if you're between snaps, and the fit isn't right, there'd be space for leakage around the legs.