Short of an official response, if we ignore the web shield transparent proxy for a minute and concentrate the variable ZoneAlarmCompatibility and its two values, 0 and 1, Zero 0 usually means off and One 1 usually means on.
So what are we switching on or off, the ZoneAlarmCompatibility, so how do we achieve this compatibility with ZA Pro, by disabling the web shield proxy.
With ZoneAlarmCompatibility=1, enable compatibility with ZA Pro we must disable the web shield proxy.
With ZoneAlarmCompatibility=0 we don't need to enable compatibility with ZA Pro, so we don't need to disable the web shield proxy. So we effectively maintain the status quo and leave the web shield proxy on (default setting), so we don't really need the ZoneAlarmCompatibility=0 line entry because it changes nothing from the web shield default.