Never saw it in patchnotes or whatever, seems like they changed it this patch or even a while ago.
Put W on the enemy and you will get only 1 Proc of Spellthiefs . Maybe they coded the new W a bit different . TY rito
reproducibility: 10/10
They made a change a very long time ago for stuff like this to make them only being able to proc the tribute every 1.25 seconds after each other. Not a bug.
http://leagueoflegends.wikia.com/wiki/Spellthief%27s_Edge it says here that it consumes one per cast adn area damage consumes one per enemy. So no, it is not a bug. Got changed like that intentionaly.
