Singed poisonous gas trail goes invisible

Singed, when he uses his poisonous gas trail and goes into a bush or vision of him is lost, so are all parts of his gas trail. Just because he is not visible doesnt mean his trail should go invisible too since vision of him is lost. I can understand certain aoe abilties not visible when used in a bush. But singed trail is continuously left behind him, and if he started it outside the bush, i should see the trail leading to the bush since i saw him run into the bush. Instead that whole trail that was there leading to the bush now becomes invisible with him?!?! It makes no sense to me and I think it is being exploited by people who know how to play singed well.