[Gameplay] Zilean Passive does not work as worded.

I have been playing Zilean in the botlane with a partner for the past few games. Each time, I level my ally up to level two with my passive, which levels me up level two with my partner, however by the time I can use my passive again, to level my ally up to level 6, I activate it by clicking on my ally, they get leveled up to six, and I am still halfway through level 5. I never move out of experience range, yet my ally and I don't get the same experience from minions or my passive.

Either his passive is bugged, or zilean gets less experience than normal, which does not seem to be the case as I hit 6 at approximately the same time as my opponents why I play Zilean midlane. The passive states that the same experience given is returned to Zilean, where is it obviously not what is going on.