I found an interesting reference in A. C. Burnell's The Ordinances of Manu, (Intro. p. xxxvii) to a work titled Anācāranirṇaya composed in Kerala to discuss "deviations" from Brahmanical Dharmaśāstras. According the footnote on this page, this work was evidently attributed to Śaṅkara. This may be the source of Śāmaśāstrī Draviḍa Dvivedi using the expression ācāryaśāpadagdha to refer to these regions. Here is the passage from Burnell:
I wonder if anyone has come across this work titled Anācāranirṇaya. Any help?
Madhav Deshpande
Ann Arbor, Michigan, USA