Ignite bug

So, I play a game against a wukong, and I decided to take ignite so before he could w I could ignite, and be given vision. However, what I went on to notice was whenever I was able to ignite him before his w went off, I was not granted vision of him. I am wondering if being granted vision is only when he goes into the fog of war, or into a bush, and not when someone like wukong stealths for a short time. Or, if this is just a bug with ignite. Thank you.