Ignite Did Not Reveal Wukong when he went into stealth.

On Dominion I played as volibear and I had targeted wukong with ignite to engage him without worrying about his stealth when he decoys. he decoyed and was not revealed while he had been ignited before. I read the description for ignite and it reveals for 5 seconds shouldnt he have stayed revealed? Note he had no Cleanse Or Quicksilver to remove affects.