Kashrut & Shabbat

Question

Rabbi, A question was recently posed to me by a friend and I am unsure of the answer. Here in Cincinnati we have a kosher Dunk N Donuts that remains open on Shabbat. The business is Jewish owned. The question is as follows: Does the fact that the business stays open on Shabbat negate kashrut? Thank you in advance for your insight to this question. Shalom, Nachshon