Maybe its not a bug,but I did it 3x with the same result.

Placing blocks under,(trying to update the area),but nothing.

Then it disappears, after 15-20 seconds.

Steps to Reproduce:

 watch the video.

OR

Go to the End.

Find a place at least 10 block above ground.

put a water bucket, destroy the water stream with any block.

Look if the water goes away.

Observed Result: the water remain there for more than 10 seconds.

Expected Result: the water should go away.

LG G7      Android 9   4GB RAM