Why is SMS to contact group not using contact's default number? Sends to wrong number
The reason is that the existing conversation thread for contact group ABC has hard-coded knowledge of the phone numbers used, rather than a reference to the contacts. Therefore after setting a new default number for contact A, texting group ABC using the existing conversation thread will send to A's old number. However, texting group ABC by creating a new message and selecting the group from contacts will send to A's new number as expected.