I am not sure if this is intentioned but here it goes.
When I logged in today I forgot that iw already enchanted my boots. Since I was playing arena i had minor run speed and +15 stamina. But since arena ended I wanted to go 4 nitro-boost. I bought mats and enchanted the boots with nitro-boost. Then I saw that the 2 enchants had stacked. I did reforge the item before I re-enchanted the item but im not sure if thats needed. This worked for me on head,gloves,feet and back.
If this is a repost or that its supposed to be like this I apologize
Iflexqt 6):