I am in a world while trying to break bedrock using the exploit, not this bug. When I was stacking up I pressed f and right click at the same time. For some reason it didn't let me place the block, but instead just switch the item to the offhand. The cause might be because the game doesn't know which hand you're using while placing the block or the game has trouble moving the item and have it be used at the same time. This bug doesn't apply when you place a block in your off hand while switching back to your main hand.

Note: I have trouble getting the screen to show up when I record an issue on OBS.