World-gen water in town wells does not flow

The water in town wells does not flow as expected when you remove a block with a bucket.

Steps to reproduce:

• Start new world

• Find village

• Use bucket to remove water block from well
  Expected result: Water flows into the gap
  Actual result: Gap remains as air block

You can remove one, two or three blocks of water in this way.

If you place a layer of solid blocks under the top level of water, to make it one block deep, the result is unchanged.