Thanks for the Bailey info. While the PLC5 was limited, the ControlLogix implementation is much more full-featured. AB partnered with Honeywell on portions of PlantScape and picked up some process knowledge from them. I'm from a DCS background and have been quite pleased with AB's ControlLogix PIDE function block, at least up to this current issue.
AB does have features to handle reset windup, which I think are pretty common with all the major vendors these days. Not so sure about "proportional windup", which is what I'm calling this problem with unclipped proportional contributions to the final output.