Recently I found multiple two-handed scythes where the ones with item level 747 have +29,5% Summoning Damage and the ones with item level 750 have just +28,0% Summoning Damage, so a higher item level comes with a lower damage bonus in this case
I’m not sure if there’s some hidden math behind this, and I didn’t check other weapon types yet, but at a first glance it seems more like a bug
EDIT 1:
This seems to be true for other weapon types as well, as a vendor just had two one-handed axes for sale, a magic one with item level 729 having +14,4% Damage Over Time and a rare one with item level 750 having +14,0% Damage Over Time
EDIT 2:
The same is true for one-handed scythes, one with item level 732 has +14,5% Summoning Damage and one with item level 750 has +14,0% Summoning Damage
EDIT 3:
For lower item levels, the affix values seem to scale as expected though. A one-handed sword with item level 745 has +13,5% Critical Strike Damage whereas one with item level 749 has +13,6% Critical Strike Damage and a two-handed axe with item level 727 has +28,7% Damage Over Time whereas one with item level 741 has +29,3% Damage Over Time
Based on this, the bug just seems to affect items with item level 750
EDIT 4:
The Stats & Materials overview reflects those numbers as well, so it’s not just an issue with the item tooltips
EDIT 5:
Necroing this thread, as this bug is still a thing, even in 2.1.0.61504
In addition, this also seems to occur on certain mid-range item levels, where items with higher item level have lower inherent weapon type affixes