Highly exploitable XP bug that has yet to be addressed

If someone goes AFK for more than 1' the rest of the team gets 5% bonus XP from all sources. This can be easily exploited allowing top and mid laners to hit level 2 at the very first wave. To make matters worse, this isn't even mentioned anywhere --not even on League's wiki page; I only read about this on reddit.

How am I supposed to know whether the enemy jungler is AFK? Please increase the activation threshold of this XP buff so it cannot be exploited like this...