Guild Wars 2

v2/account/masteries returns for each track
either nothing if current level is 0 (that is correct)
either the max level minus 1 of the track instead of the actual level for the account

Dorazur.9420:

either the max level minus 1 of the track instead of the actual level for the account

That is right, because the first level is 0, so if a mastery has 5 levels you make a FOR cicle like this:
for (x=0; x < mastery.levels.length; x++)
In the example it would be for (x=0; x < 5; x++) , so x goes from 0 to 4 that are exactly five levels (0,1,2,3,4).

The issue is not the minus 1 but the level returned is always the last (saying n-1) instead of the actual which can be in range 0 to n-1

I see no change yet. Has the deploy been done ?