Our 99 is the same way, but seems to plug the fill hole. When I first discovered it, I was worried and the dealer invited me to just buy a new dipstick. I never got around to it, and haven't had a problem 4 years. I give it a good look when I change the oil and it never looks different and doesn't leak.
01 Ford Ranger 4.0 SOHC V6, 4x4 - Mobil 1 High Mileage 5w-30, Motorcraft FL820s