Guild Wars 2

On my lv 16 character, i decided to refine some of the low level mats to get a few levels on him.

L1 Leatherworker. So I made a leather square. My character XP didn’t increase.
I tried Bolt of Jute. Got some xp.
Tried another Jute. No xp.
Tried another with critical success. No xp.
Tried another with non-crit. Got some xp.

Did a bunch more, paying attention, and got xp on 1 more non-crit, and on 1 crit. About 5 more gave none.

Is this not a bug?

Your character will only gain xp every time you gain a new crafting level (as seen at the top of the crafting screen) between 0 and 400.