I have this on my paladin, so here are some notes:
- Casting sacred shield will cause the proc to go off (making your heals start to absorb). Not sure if the proc from sacred shield can proc the mace.
- The healing over time from your flash of light adds to the mace's shield on the target when your mace is proc'd.
- Heals on yourself from your JoL cause the shield on you, but not on anyone else. Still unsure if the healing from JoL can trigger the mace proc.
- Healing caused by trinkets do not trigger the shield effect, pretty sure they also do not cause the mace proc (tested using Living Ice Crystals).
- Healing from your Glyph of Holy Light triggers the shield (which makes your raid look really cool ^_^ )
- You do not have to cast an effective heal in order to proc the mace (healing a target at 100% will proc the mace)
Let me know if I missed anything to test.