The bug is that when in creative you select empty bucket and milk a cow so than the icon will be of milk bucket not empty bucket and you can not remove water. You guys have to check it out and fix it

What I expected to happen was...:
That there should be a milk bucket and empty bucket too. like different

What actually happened was...:
That in creative empty bucket and when it's milk by cow it than change into milk bucket not empty bucket and than you can not Pick up water