If you had your stereo system turned on and then it was turned off not by you (ran out of power) - the music CD you inserted disappears.
What’s the deal with music CDs anyway?
Do they have a reason to exist? Do they have a reason to automatically get ejected when stereo is turned off? It seems that their only role is limiting access to stereo systems.
Even nowadays CDs are pretty much ancient tech, like floppies were 10 years ago.