Executing a chat command or pressing enter in a command block while looking at/holding an item/block with a right-click action performs the right-click action of the block/item

Put the summary of the bug you're having here

What I expected to happen was...:
Only the command gets executed.

What actually happened was...:
The command executed and the block's right click action activates

Steps to Reproduce:
1) Go into creative mode
2) Fly up 2-3 blocks and look at the ground
3) Hold a full water bucket in your main hand
4) Execute /gamemode 0
5) As you are falling, you should notice water appears even though you did not right-click on the water bucket.