It is normal with Dexters. Some bloodlines seem to produce more split ears then others. I bred a British white heifer to a Dexter bull last year and her calf has split ears. It surpized the heck out of me because of the cross breeding. That same bull threw another calf that has flower shaped ears.
Dexter poeple have not culled the cattle the same way others have and for some reason this ear does not bother most of them. I can not stand it. To me it is a mutation.