This glitch has existed for a very long time, and I'm surprised that it still hasn't been fixed. In any version of Minecraft Bedrock Editon, you have the default commands /w, /whisper, and /msg. All of these commands have the same function, private message a player in a world or server. But the problem is, those private messages are public unless you set /gamerule sendCommandFeedback to false. But you need cheats on in order to do that! Plus on a Minecraft realm, the owner of the realm can see all the private messages. This defeats the purpose of even having private messages in the first place. You might as well publicly chat unless cheats are on. This seriously needs to be fixed. 

 Note: All of this happens in the bedrock edition of Minecraft, and has been happening as early as version 1.6.0.