If you're in the editor, and attempt to simulate, but are stopped by the message that there is no pilot or probe core, then the next time you launch an actual flight, the game still acts like it's a simulation, to the point of having the cost counter in the corner, disabling "Recover Vessel", and making the pause menu the simulation menu. However, if you click "Terminate Simulation" the cost counter goes away and the normal pause menu returns, although the dropdown at the top of the screen still won't appear.
If you're in the editor, and attempt to simulate, but are stopped by the message that there is no pilot or probe core, then the next time you launch an actual flight, the game still acts like it's a simulation, to the point of having the cost counter in the corner, disabling "Recover Vessel", and making the pause menu the simulation menu. However, if you click "Terminate Simulation" the cost counter goes away and the normal pause menu returns, although the dropdown at the top of the screen still won't appear.