Don't think it's a bug, little point in materia under level 20, as gear is replaced quickly, and the two level 41+ represent the endgame quality levels. This is evidenced by the drop positions of the catalysts, T1 Cats are in Rank 3 gathering nodes, T2 in rank 4, and the rest are in various rank 5+ nodes. I.E. Don't bother with em (except for blowing up your cheap 1-20 gear for materia) until you hit 20ish.