I always have a few that act that way, as well. As long as the tap root is getting enough moisture they will keep plumping up, whether above or below ground. Sometimes I'll push the soil up around the root just to make myself feel better.
I seem to have an exception to that this year with French Breakfast radish. They are more pear shaped when the top is above the soil line. I don't know if that's normal or not. I don't think I'll be growing that variety again.
cocoa, yes, that's the shape of the French Breakfast. We LOVE the taste of that one, it's exta spicey. If you have leftover seeds I'll take them off your hands and trade you any others I have. I may have some Cherry Radish seeds, will have to check.