While I'm no expert in this and have not personally attempted it, pretty much most modern vehicles (with auto transmissions) are drive by wire - so by moving the "shifter", you're not physically shifting anything in the gearbox, rather instructing the electronics system (on-board computer) to do it on your behalf. I'm positive there is a line of code in the system's programming, somewhere, to prevent it from actually attempting a physical reverse shift at a forward speed.