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.
Cannot reproduce this.
Please demonstrate the issue in a video recording or explain in better detail why this is occurring. To re-iterate:
I went into creative
I got a water bucket
I flew up a few blocks, but still low enough that I was within clicking distance of the ground (the black box appears around the box)
I type /gamemode 0
I fall–nothing happens
I've attached screenshots of the setup and end-result