I think that it is intentional for the first one to disappear, because the limit is 2 or 3 wards at a time
I don't think a limiter is nessary, because if you play support you should know when your wards are timing out and were / when u placed the wards
And the addation of a limiter might actually be a detrement because what if they need to place a ward to secure a kill or save their life, there is a trade off in having a freash ward vs having one disapear,
For example, a champ that might buy this itemcould be lee sin (going a supportish off-tank role) he could use the wards to jump close for ganks or to escape over a wall with safeguard, Placing a limiter would not allow higher levels of play .
I hope i awnsered your question without going off on too much of a tangent