Azir Passive Bug

In a normal pvp game I've played against an and he used his passive at one point in the game and the health bar on the tower was surrounded in blue, like there was the health and around the bar was just a blue rectangle in the background where the health bar is,and i'm not sure if this bug has been dealt with but it doesn't do this every time but i'll try to get a screenshot of it if it happens again or if i figure it out in a custom or something.

If you do understand what i am saying then you i think others might be able to describe it more or give screenshots of it.