To clarify how it used to work.

Before starting the simulation, with the Start button, it was possible to use the Shift key, and it would start the simulation. It was useful.

After stopping the simulation (with the Stop button), it was possible to use the Shift to continue the simulation.

Pressing the Shift whilst the simulation was running would move to the mode that allowed the dragging of the simulate (item being simulated). The simulation would always stop when releasing the Shift key, although it would still say it was running, and the button to stop the simulation was still active. It was definitely not running though.

At any time, obviously, one could grab some part of the simulate and drag it about.

Now, the only way to drag the simulate is while the simulation is running; releasing the Shift key no longer turns off the simulation; it seemed to be a bug, the fact the simulation stopped, and the buttons didn't change to reflect that - I remember posting about this weeks or months ago.