The classification of Bidah (i.e., innovation in religion) into praiseworthy & blameworthy or into obligatory, recommended, permissible, disliked, forbidden and such are well established by majority of scholars among all four schools of Sunni Islam. The scholars have agreed that not all innovation is evil and a matter not existing during the time of the Salaf does not necessarily imply the rejection of the matter. Instead they have explained that if an innovated matter has a basis in Quran, Sunnah, Ijma, Qiyas or other sources of evidences in the Sharia either in general or detail, than such a matter is not necessarily rejected. What follows then is an ijthihad done by scholars in categorizing an innovated matter into one of these classifications of Bidah and as a result it is natural that there exist at times difference of opinion among mujtahid scholars within a school as well as across the schools, in their conclusions because of the difference in weighing of evidence, applying the principles of fiqh and so forth.
However there is also another sub category whereby an innovated matter has no clear basis in the sharia nor rejected by the Sharia or a case where an innovated matter has a basis in Sharia however it was not acted upon by the Salaf or that that no specific form is known from the Salaf with regards to it. The Maliki scholar Shaykh Uthman Don Fodio in his book “Ihya’u as-Sunna wa Ikhmad al-Bid`a” goes onto mention the existence of a difference between Imam Malik and Imam Shafi on this, may Allah be pleased with them all.
Similarly elsewhere the Imam says,
Quotes taken from the book Ihya’u as-Sunna wa Ikhmad al-Bid`a : http://siiasi.org/wp-content/uploads/2014/12/Ihyas-Sunna_wa_Ikhmadl-Bida_The_Revival.pdf