[The_Think_Tanker]

Just tested this myself on my copy of WinSPMBT v16-Extended and WinSPWW2 v15-Extended. In both pressing the '8' key to reverse worked immediately and required no holding-down of the key in any instance to work.

I tested a range of vehicles and it seemed to work each and every time I tested it, including the appropriate "[Vehicle] could not reverse!" when there were insufficient movement points available.

I do recall it being a little more finnicky in some of my older versions back when I only had the freebie version of WinSPWW2...but that's only a vague recollection and I would have to check to be more certain.