This same thing has happened to me when I baked in either shaped pans or bowls or very large pans - and also whenever I bake a cake with pudding added to it or other liquids that add flavor & moisture. My skewer will come out clean, but when the cake is cooled & I start working with it, I discover that it's REALLY moist in the center. I taste a teeny bit of it & unless it tastes like raw batter (which is usually a much different taste from a "done" cake) I consider the fact of the added moisture or pudding in the batter. I'm thinking that the pudding or other liquids in the mix just maybe gravitate toward the middle of the cake for some reason....or maybe because of the shape/size of the pan or whatever you use to bake it in just makes the middle part take longer to cook, so what you get is a middle that's technically done but really moist becuase the extra liquids or whatever didn't completely evaporate or something into the rest of the cake?? These are just theories!! lol
I say as long as it's not doughy and doesn't smell/taste like the raw batter, then it's probably ok!! HA!