@cyberdragon442(View Post) You never re-opened it, the save was never destroyed, you just saw it how you left it off. When you open a save and then go to the online save browser, the way you left the simulation is still there, and hitting X to close it will bring you back to what you were working on or viewing before.
Please don't use all caps ever again, and give more information next time, like a save id.