Different message is displayed, instead of no permission

I was typing in some commands to check whether my world has cheats enabled. When I type in /gamemode creative, it popped out a different message, which is "Unknown command at position 0: <--[HERE]". This means that /gamemode is no longer a command...

What I expected to happen was...:
The "You do not have permission to use this command" message should be displayed.

What actually happened was...:
Instead, the message "Unknown command at position 0: <--[HERE]".

Steps to Reproduce:
1. Create a world with cheats disabled.
2. Type in "/gamemode creative" (or any other commands that need cheats to work)
3. Notice that the message "Unknown command at position 0: <--[HERE]" was displayed instead of "You do not have permission to use this command". How am I supposed to know what am I typing wrong?