The pickup animation is different when filling a bucket and the filled bucket is placed in a separate item stack.

How to reproduce:

Method #1:

1. Place water, lava or powder snow.
2. Give yourself an empty bucket and remove all filled buckets from your inventory.
3. Switch to Creative mode.
4. Use the empty bucket on the block or fluid you placed.

Method #2:

1. Place water, lava or powder snow.
2. Give yourself a stack of empty buckets.
3. Use the stack of empty buckets on the block or fluid you placed.