Yellow Trinket Wards Disappearing in Presence of Pink Wards?

I haven't seen anyone else report this so I'm not sure if its just happening to me or if there's some new ward functionality that happened in preseason patch that I don't know about

Anyways, what is happening is that when I play mid lane I like to have a pink ward in one of the bushes on the side of the mid lane. Sometimes (this has happened more than once in multiple games) I will see the enemy laner place a yellow trinket ward from over the wall into the bush, and then after a second or so it will completely disappear like if there was no pink ward there at all! But it seems like the invisible ward will still provide vision to the enemy because I have seen them clear my pink ward from outside the bush even though my pink ward is not revealing any enemy wards in the bush. It is very annoying because even though it may look like they have no wards in the river to my jungler, they still may be able to see him coming in a gank.