Jungle Creeps Regen Health Bug

So this has happened quite a few times to me now, I start attacking a jungle creep, and when I smite it, it starts regenerating health rapidly, even when I'm still on it and in range. So I will have to wait for it to regenerating to full health and then try again, therefore wasting my smite. Here's a little breakdown of what happens:

1. I smite a jungle creep first
2. I start hitting it and it
3. It starts regenerating health back rapidly, a bit like when syndra brings the blue buff out of its area, accept I do not leave the area
4. I have to wait for it to get back to full hp before I can kill it