Crafting Bug?
This was changed back when they introduced ascended weapons and a maximal crafting level of 500.
Seeing as how extremely expensive getting from 400 to 500 is, I don’t really see why that was necessary. But yeah, they’ve changed it to avoid people getting more than 10 levels from maxing out one crafting profession. This also was changed already for those professions which can not be leveled to 500 yet.