Lay on hands going on CD not used

Hi all, So I play prot pally, and this thing happened to me twice: basically, when I want to use LoH, it doesn't work and when I check, it was already recharging though it had not be used once. The two times it happened the healer was a priest, so maybe it has something to do with the class? Anyway, if anyone knows what's the deal, I'd like some help please