To reproduce, fill your inventory with arbitrary blocks and put a stack of empty buckets/glass bottles in your hotbar. Use it on a cow/water/lava and observe how you throw out filled bottles/buckets instead of filling your offhand slot first.
Linked issues
relates to 1
Attachments
Comments 22
Is this still an issue in the latest snapshot 16w44a? If so please update the affected versions.
This is an automated comment on any open or reopened issue with out-of-date affected versions.
As RobinDinVienna said, the offhand slot is not intended to be used for picking up items, the only way for items to be placed in the offhand slot is if it is done manually by the player.
Relates to MC-84849