Hello malungu,
No need to delete the message or the topic.
I will explain a bit further on why this has happened in case anyone else encounters the same in the future.
The Full screen mode is initially with all tool bars hidden, but they are still accessible, and using the F8, F9 and F11 keys you can toggle the toolbars so that you can e.g. do a quick marking without exiting full screen, and then continue reading. If you exit the Full Screen mode with some/all of the toolbars visible, this would be remembered and the next time you press F12 you might be surprised

but the behaviour is as it should and is expected.
Best,
Stefan