mana never fully regenerates

i've had this problem for at least the past 3 major patches

i play a lich, and i currently have 1928 mana at full,

but it never regens to that number, it only goes up to 1925, and this number scales depending on how much mana i have (gets worse)

it is by no means game breaking but it is very frustrating

this is my second time posting this issue