I just played an opponent in the Silver Arena who appears to have found (and is exploiting to the fullest) a possible bug using a combination of Sanctuary, Shard of Divinity and Miracle. He had 463 max HP when I finally decked out. If this isn't a bug, it needs major adjustment. Thanks.
Shard of Divinity will raise your health by 24 if you're using a light mark -- your TOTAL health. That means he may as well have used several of those to raise his health, specially when you consider that he was in silver and that he could have as well used dexterity to get ~12 SoD's.
Further on, even if he did not have Double Draw, he could have invested all his points into health points, which means
200 + 288 = 488 total (possible) health. It is not ridiculous to assume he may have drawn several of his SoD's as you "decked out". This is most likely not a bug unless his healing artifacts (As in sanctuary) were raising his max Health (and not just healing him.)
488-24 = 464, so him having 463 health is not impossible. Specially because you yourself said "Miracle" -- he just used miracle before he died and got ~463 health points, which is 200 hp + 5 SoD's -1 Hitpoint (200+264= 464; 464 - 1 hitpoint due to miracle effect = 463.)
Most likely not a bug.