I'm not sure if this is correct. Pius XI seems to go beyond the boundaries of "sin" in Casti Connubii:
This subjection, however, does not deny or take away the liberty which fully belongs to the woman both in view of her dignity as a human person, and in view of her most noble office as wife and mother and companion; nor does it bid her obey her husband's every request if not in harmony with right reason or with the dignity due to the wife; (CC 27)
And there's the rub, gbc. And the reason that JPII encourages "mutual submission." It's a matter of perspective. They both seem to be saying the same thing, with different emphases.
"This subjection, however, does not deny or take away the liberty which fully belongs to the woman both in view of her dignity as a human person, and in view of her most noble office as wife and mother and companion; nor does it bid her obey her husband's every request if not in harmony with right reason or with the dignity due to the wife"
Commands "not in harmony with right reason or with the dignity due to the wife" would involve sin.
Of course, traditionalists who use the same justification for not giving blind obedience to everything that comes out of the Vatican are often accused of "schism" or worse.
It could be legitimately argued that many of the changes "mandated" at Vatican 2 are not "in harmony with right reason" and therefore not subject to obedience.