Green and Pink ward vision bugs?

Pink ward vision seems really inconsistent. On certain parts of Summoners rift a Pink ward can see enemy wards really far away (notably edge of bush behind red buff and edge of bush by wall in front of red buff) but there are other places where the pink can't see a closer ward (edge of small river bush and edge of bush above/below small river bush). I'm not sure what's going on there but it's been bothering me for a while.

When you use an upgraded sweeper you need to walk into a bush in order to see an enemy ward in it even though you have your own ward in there. Sweep one bush, with oracles sight walk near another bush that has your own ward, no visible enemy ward, walk into said bush, visible enemy ward.