[GAMEPLAY] Dragon reset

At IEM, in the second game of GMB vs CLG the dragon resets and starts to regen health for whatever reason when it has no reason to reset. The buff from dragon could have effected the outcome of the game if CLG had gotten the dragon. Because of the hp regen of dragon, It allowed GMB to group and for Diamondprox's Q to come off cooldown to steal dragon. No one has addressed this. Is this working as intended or what?

I do not know what causes the bug. It has never happened to me in game, but this video clearly shows the bug.

https://www.youtube.com/watch?v=WCm8vrKMong&feature=youtu.be