http://youtu.be/akxqOJ1kzKA (also contains another bug I am also reporting in another issue)
place a water bucket anywhere
hold the now empty bucket in the offhand slot, and the empty bottle in the main hand.
Put your cursor just above the water, then quickly flick your camera down, right click, and flick it back up as fast as possible.
Often, but not all the time, both will fill and the water source will go into the bucket.
Comments 3
@redstonehelper This bug has been resolved, however this procedure now causes a ghost filled water bucket instead - without removing the water source (a "Water bucket" that appears full until you attempt to place the water, but the water disappears and the water bucket returns to an empty bucket)
Marking fixed then (in some version between 15w31c and 15w44b), the bug you're experiencing now is probably caused by MC-90022.
Is this still an issue in 15w44b? If so, please update the list of affected versions.