So here's a bug I found. It's a little obscure, but I wanted to report it as it didn't get fixed in 1.8.1... I thought somebody would've noticed.
Anyways, in Creative Mode, if you stay under water for a long time, you'll start seeing bubbles come out of your face. Now, in Survival Mode, this would indicate drowning and would be paired up with you getting hurt, but since in Creative Mode there's no health, or oxygen meter for that matter, you only see these bubbles.
Here's a picture I caught of it, although you'll just have to try it yourself.
I would say that's a useful feature. This way you can build something in creative underwater and have an indication on how far you will get before drowning.
It's a bug because it's something they overlooked when implementing Creative Mode.
That's like saying only having to place ladders every other block wasn't a bug. People found it useful, as you needed half as much ladders as you do now (but not half as much materials, though), but it was still a bug.
If you want to see how far you'll go before you start drowning, this is not a good way. Besides, if you're building in creative mode, why would you need to know how far you'll go before drowning?