You have to have the bottle you want filled up in your hand, then switch to the other bottle in your hand. Not really a bug, seems pretty realistic to me.

Just right click on the respective bottle and say "Take into hands".

If you want to go by action bar, the bottle you want to fill has to be more left or upper in your inventory, because the engine allways picks the <i><b>first</b></i> one in your inventory.

For instance, if you've got one bottle in your pants and the second one in your backpack, the action button will <i>allways</i> take that one in your pants, because in your inventory, the pants are <i>higher</i> than your backpack.

Regards
Johnny

Or drop the 1st filled bottle on the ground and pick up after filling the 2nd bottle?

This has been reported previously at #717

Duplicate of #9 (Hotbar (Using Non specific item)).

Please use the search function to check if an issue already exists before posting a new one.

Refer to the original to provide additional information on the issue.

Regards,
Johnny