Players cant pick up a water source with water bucket when inside the flowing (down) water.

Reproduce :
1. Tower up
2. Place a waterbucket at the edge of the toppest block(there should be a flowing water)
3. Climb up in the flowing water
4. Try to pick up the water source using an empty bucket
5. You cannot pick the water up inside the flowing water unless the player is exposed out of the water