Amelioration Omen doesnt trigger many times

I've had many cases where the Omen of Amelioration is in my inventory & activated (with a border around it), but doesnt trigger and I lose 10% exp. I noticed this is when I have a stack of them highlighted, and a previous one triggered, the next one sometimes will not trigger. I have to right click to deactivate, and activate again. Seems then to work.