Water bubbles can appear out of flowing water

I created a 2 wide empty column with one block of soulsand at the bottom.
I put a bucket of water at the top, creating a 2 wide water fall.
I removed the source.

The water with bubbles don't disappeared. It can't be removed using a bucket ether.

I removed the block of soulsand.

Now the water can be taken, but the column is full of sources.