John C.
From Roll20 Wiki
Whispers
In our game, whenever we use the "/w" command in text, the GM ALSO receives a copy of the whispered chat. So, for example, if two players want to make a plan without the DM/GM's knowledge by using a whisper, they can't. Both players PLUS the GM will receive a copy of the whispered text.
Or, as in the example on this page, if someone is asking someone else where the Cheetos are, the GM would see it in the chat.
According to the Wiki, this means our whisper is NOT working as intended.