Holy Word: Sanctuary (Prayer of Healing) - Blesses the ground with Divine Light, healing all within it for 449 every 2 for 18 sec. Only one Sanctuary can be active at any one time.
The worst part about this bug is that only one is active indeed, but there's only one way to know if you're standing in the active one and that is looking at your scrolling combat text. If there are multiple up, it's sort of guesswork which one to stand in. It's always the most recent one that is actually doing the healing btw.