Is Elder Dragon in-combat regen intentional?

When fighting Elder dragon, I noticed that it regens HP even while I am attacking it (and no one had leashed it yet). Is this intentional? The in-combat regen makes Elder Dragon far bulkier than usual and makes it harder to smite properly. This feels like an oversight, but I am not sure; since Baron Nashor doesn't regen HP in combat. Perhaps the in-combat regen is why some LCS casters consider Elder Dragon to be harder to kill than Baron. Elder regen in action.