Looking at how some of you get to my site, I stumbled across the Fern and Faerie Sew Diapers for $30 or less site.
Although I'm not too into the making them pretty, it did have a fix for using a Snappi for my t-shirt diapers. I have moved on to making a velcro belt fastener which I like better (Not as scary and can be used sans diaper cover without grabbing onto furniture), but when I was using a snappi, they didn't always hold onto the tshirt diaper very well. It suggests making a layer of "snappiable" fabric to the diaper. I will have to make one with my version to see how it goes.