If the development of another product (1) causes something to break in yours because of the way your product was built ages ago, (2) causes users a lot of pain and they blame you for it, what do you do?
You can’t just blame the last person, because admit it, you wouldn’t have foreseen it too. And also its an excuse to shift blame and relinquish some responsibility.
My attempt – accept it was an oversight, apologize, explain, learn something new to anticipate, and press on to make it better. It’s your baby now.