Water turns invisible.

I was making a farm in the first 20 minutes of a new world and I chose to cover my water with dirt. when I tilled the land next to the water, I could see into the space via the indentation of the tilled block. I could not see any water, but when I broke the dirt block above the water suddently became visible for 1 block in either direction.

 

Just thought I'd report this.

Thanks!