You're right, it wasn't the software as such (more like the design of the system).

I just read more about PIO and it's funny, it reminds me of a short story I read a long long time ago, written by Arthur C Clarke, I remember the scene in it where a pilot is remote controlling his big space ship or plane of some kind, while standing on the ground. But because the remote is going through a satellite, there is a feed back delay, say 1 second or so. So when he tries to compensate for a wrong turn, a flavor of PIO is induced and the ship crashes. Think that particular story was written in the 40's, good foresight of Mr. Clarke.