Griffin - Medusa Spell bug?

Every time I play with Perseus and I try to petrifiy the Griffin with the Medusa spell after he lands, he won’t get petrified. Look in the video from 0:45, for better understanding.
This is not a 1 time occasion, it happens every time. If I use the spell before he gets in the air, it works. Does he have an immunity for a few seconds after he lands or is it a bug? 
 

 

Hey Tzogos,

The Griffin must have landed completely before you can petrify it.

In your video, the Griffin just made his stomp attack and was still considered as flying which explains why it didn’t get petrified.