Gel STAINS are a little different, you will see some liquid form on the top and it is best to stir them up a little. If you don't you can get what you witnessed as some of can go on thinner. Most all gel stains also have a "little", varnish in them also over longer periods of time they can skim over also but typically not anything near as quickly as gel varnishes.
And since you mentioned unsanded oak, gels do much better on sanded surfaces, because they go on thick they can really vary in shade. It is hard to wipe out the more coarse areas on the wood. I learned this 20 or so years ago by trying to take a short cut.