Power up when dead bug

Hi,

Today I was training in a friendly gym and my Flareon could't beat the friendly Venusar. He died and I power him up while dead in order to have more chances of beating the Venausaur.

To mi surprise when I power him up He got some CP and 1 HP point and and went from 0 of X HP to 1 of X+1 (I don't remeber how much it was)

Basically it revived and I just healed him with an hyper potion and was ready to go.

Don't know if it's a know bug but it can be really useful in times of need