Without the book cover for reference, maybe Bob D. was playing a
multi-progressive? He had one of those 129 coin quads.
It just bugs me when this happens and I have to add a coin or two to
get to 5 coin increments on the credit meter.
Another theory is he was just about to get some loose change for the
cocktailer. I do this on .50 machines, put in a couple bucks for 4
credits and cash out.