Not sure if this was changed in the patch, but this thing would just proc at seemingly random times. Often when I was running through a zone invis, it would just go off for no apparent reason, and cause invis to drop. So I had to get rid of it. If this has changed someone please post here.
It also had wierd stacking issues with my twincast AA. While I equip this shield, if I click my twincast AA, the timer on the AA never starts - it's as if I never pressed it, so I could keep pressing it over and over and I still get the buff up that I am twincasting. HOWEVER, my spells did not twincast even though the buff symbol was up, so this thing was really ******** it up.