A while back, someone glitched a source block of water on top of the slabs (during the old plugin). Now when I placed something next to it the source updated causing this: http://prntscr.com/bi6ads . Any ideas how to get rid of it? I have tried: using a bucket, using a piston to push a block into it, using a piston to put the piston head in the water, using lava to turn the water into stone. None of them worked.
Solved. For those who have this problem. Use a dispenser with a empty bucket and power it with redstone.