Assassin perma vanish?

So I was playing as my assassin and randomly out of nowhere my vanish gets glitched. Basically what happened was mana regen still worked while in vanish, including the 1 per second thing which canceled out the -1/s of vanish.
It stayed if I tried to vanish again but left when I /class’d
I didn’t think too much of it, but a couple hours later in the same day it happened again.

Just curious if this has happened to anyone else/is a well known thing or not, or if anyone knows why this happened.