User blog comment:Fistful of Force/Quick post: Supports, learn how to place wards on terrain./@comment-206.174.24.215-20130324200512/@comment-81.233.51.169-20130325115049

If you get caught it's none other than your own fault, generally speaking.

Also, this isn't bug abuse at all, it is how impassable terrain was programmed to interract with objects that would be affected by said terrain. It goes for everything that can be placed inside impassable terrain, from Champions themselves to wards to Shrooms or Turrets. If they are placed inside they will be pushed out to the closest passable terrain.

Try it out yourself with the summoner Flash.