Converting item level 70 equipment

I haven't spiritbonded for a while now, so I may not be up to date with recent developments concerning converting materia.

Back with 2.1 I remember converting item level 70 equipment and always got grade 4 materia out of it. I converted a full vanya set and two gryphonskin sets (bard and monk sets) and several rose gold accessories. I always received a grade 4 materia.

Today I crafted a full Vanya set again with the accessories to go and converted them when I could. This resulted in:
8 grade 3 materia
3 grade 4 materia

This is hardly any different from spiritbinding lower level equipment. Is this working as intended or is this indeed a bug?

edit: Title's wrong,

I believe this is as designed. You need to convert highest craftable gear to get 100% chance at grade 4 materia, which means that when item level 90 craftable gear was introduced, item level 70 stopped being assured grade 4. You need to convert item level 90 for that now.

i90 doesn't even give you 100% tier IV, just so you know.

Not a bug /10char