Rashba"g made a takkana in order to drive down the price of the birds for korabanos, that a woman is not chayav to bring korbanos for all vaday births. This is very difficult to understand -- how can he go against a chiyuv in the Torah for korbanos? See the Shita Mekubetzes in the back who bring the peshat of Rabbeinu Tam.
The Netziv in the Harcheiv Davar at the beginning of Parshas Tazria also grapples with this issue of Rashba"g seemingly going against halacha. To solve this problem, he says in the name of his son, Rav Chaim Berlin that we can see the peshat of Rashba"g in the pesukim of Tazria. The summary pasuk of "Zos Toras Hayoledes" is before the pasuk that addressed the poor korban. One would have thought that the order should have been reversed. Based on this, he argued that the ruling of multiple korbanos for multiple leidos is only for a rich yoledes. However if she is poor, not only does she bring a bird instead but also she only has to bring one for multiple births. Therefore when it became expensive, Rashba"g said the rest of the korbanos are no longer obligated and the yoledes only has to bring one, but should she become rich, then she would be obligated in all of them.
Thanks to my Rebbe, Rav Binyamin Tabory, may HKBH send him a refua sheleima, for pointing this Netziv out to me.