Converting item level 70 equipment

[Lyrica_Ashtine]

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,

[Kaishi]

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.

[Ronove]

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

[Lebenoshl]

Not a bug /10char