Have vision of vison wards when I shouldn't be able to

This happened twice in one game. First time I swept a ward in bot river bush and it expired before I could kill it. Naut put another ward and I still had vision of it even though the sweeper was no longer active.

Second time I swept a ward in mid bot river, Naut put another ward in what looks like the exact same location and I still had vision of it.

http://plays.tv/video/5869706559e859a9ef/ward-vision-bug?from=user

match history: http://matchhistory.na.leagueoflegends.com/en/#match-details/NA1/2388546916/19685652