Hi @lucaviness.
I have not been able to reproduce this bug.
I couldn’t figure out how to turn a post into a whisper, and then read:
Could it be that the person published a regular post, and then deleted it and recreated the message as a whisper?
That might explain the user icon appearing, since their normal post would show up, but if they delete that message it wouldn’t immediately remove their avatar from the topics list until there was a refresh. I was able to reproduce that effect.
If you are staff on the site in question, you might be able to see a log of what happened, here’s what mine looks like:
Hope that helps, and that whispers are working as expected.