Does am upgrade not always improve?

Hello,

just for fun I'm buying several fair stuff from the world.
I found out that upgrading to lvl^2 doesn't improve anything on some devices.
Is this a correct behaviour or should it be reviewed?
I think it was the pants on lvl^1 having 2 dexterity / 6 trading / 6 tactics.
On lvl^2 the values are the same. As far as I remember I also noticed in the past on another device. ?.Thank you !!

Reference www.beta.the-west.net

Example Motion Graphics Video