Sometimes you can get a vacuum seal happening from a quick temperature change with the dippers. Try chilling the bottom of the dipper in some ice water (to make it contract slightly), and then turning it over and putting the top of the dipper in warm water (to make it expand slightly). That should take the top off. Of course, if that doesn't help, or you find the top is still too tight, let us know and we can send you a replacement.
Here is short video showing you how: