It is supposed to proc on any cast, but currently only procs on direct heals.

This is like the best healing trinket for me mana-wise.

Tooltip error or bug?

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(f ;..;)f BRAINS (f ;..;)f BRAINS (f ;..;)f BRAINS ¯\(°_o/¯ OMG too many of em wtf to do?
OMG GET THEM OFF GET THEM OFF
(f ;..;)f (f ;..;)f (f ;..;)f (f ;..;)f (>Q.Q)>

-Zombifest Oct. 2008

I think it is a bug but I have resisted responding until I am 100% sure.

Update: it is a bug. We are fixing it.