0.26.3 (Though this has been going on for a while, so it’s not something you recently introduced by accident. It hasn’t always been the case, though)
Artifacts in Heritage or Item Sets are always set to whatever my first unequipped artifact is, alphabetically. Example: If I breed a new creature, and it’s parent had normal “Boots” but I had an item called “Abomination” unequipped, the artifact that will be assigned to the new creature is “Abomination.” The same goes with item sets; if I save an item set with “Boots,” when I try to equip a new creature, I get “Abomination” out.
Spell gems are unaffected by this.