I had 2 empty PET bottles in my inventory. I dragged one to quick bar No 3, and the second to quick bar No 4. When I came to a well I pressed the No 3 key and the bottle appeared in my hand as expected, I filled the bottle successfully.

I then pressed the No 4 key and instead of the second bottle being in my hands the first bottle was removed from my hands leaving my hands empty. I pressed the No 4 key again and a PET bottle appeared in my hands but it was the full one, not the empty one. Looking at the quick bar, both PET bottles were highlighted, and in the inventory the hand was shown holding the bottle assigned to Key No 3.

To make sure I had not dragged the same bottle twice to the quick bar I removed them both and then dragged them back. The problem was the same.

I Managed to fill the second bottle by dragging it into my empty hands. {F31457}