I don’t think I can repro that?
My step by step just to see if I’m doing a 
- Test_One creates post by directly replying to Test_Two
- Also throws in a quote of Test_Three and an @mention of Test_Four
- As admin, toggle that post into a whisper
The only people who can see the whisper are Admin and Test_One (which is expected, as you can see your own whisper posts even after you can no longer create whispers) [this has since been fixed see below]
Is it a page refresh thing?