This issue has existed since before (I don't remember what version it was, but I think it didn't happen when we first got that command), but because developers still didn't fix this bug, I'm reporting this.
Same with the title, you can whisper to yourself using tell (msg, w) command.

Step to reproduce
1. Join world with cheat enabled.
2. Use tell command like this: /tell (@p or your name) (message)
3. The game sends message to yourself instead of showing message You can't send message to yourself!