I just tried again with the way the previous poster recorded: making the bet -> when it wins click on something else like the bonus page or whatever -> return to coin flip -> no cash out button
When I did it the sound route I also had the same result as him.
So in other words, when you refresh the page (close the tab) this doesn't happen, when you stay on the page and just jump somewhere else and then return to the game, the bug is on.