This isn’t nearly as incongruent as you may think. First, in true BDSM relationships, the submissive is the person with the power. All it takes is one word from the submissive to stop the entire interaction. Technically, your chosen position of being a submissive falls completely in line with behaving such as you identify. You are independent to make a choice that will either continue to allow the sexual experience or stop it short. Don’t mistake me, I am operating under the presumption that you are still wholly participating as a submissive while maintaining that role; you are not just taking it without giving back and ensuring your partner is also enjoying the experience. Thus, you are still maintaining congruence with your gender equality beliefs; you are not expecting your partner to do all of the work. You are giving back to him/her via your submissiveness to help fulfill their sexual wants/needs as well. Alternately, though, do you ever find yourself desiring to be the dominant one? Switching it up every once in awhile may be a fun surprise for you both while giving you the opportunity to explore your everyday behavior in a sexual way. See if behaving in a more aggressive way during sex appeals to you and your partner. Your partner may enjoy seeing that side of you come forth in sex while allowing him/her to experience a different side simultaneously.
The other thought I have about your question in this: if you behave dominantly, independently, and through a feminist, gender equality perspective in everyday life throughout all situations, isn’t this really like a mini vacation from yourself? You obviously feel safe enough with your partner to relinquish your interpretation of control by allowing him/her to be the dominant one (even though we’ve established otherwise). Perhaps that safety translates to you being open enough to express and explore more vulnerable parts of yourself with this person. You feel free enough to be all of you with this person. All of you happens to enjoy being dominated. The release of control you perceive is like stepping outside of yourself for a break for a little while and allowing someone else to drive the proverbial car.