When you look underneath a block with a rail on top that's just above water it doesn't render the water correctly. In the screenshots, I have a texture pack on but when I took it off it had the same effect.

What's broken?

The water texture underneath a block with rails on it.

How did you break it? Or what were you doing when it broke?

I was playing normally and happened to look under my rail system and saw the water bug. 

Steps to reproduce

1.)Put a block just above the water.

2.)Put a rail on top of the block.