AB PLC FAL Instruction Problem

I have programmed AB plc's for 17 years and never come across the problem you describle. I do however use the done bit in front of my FAL instuctions.
I read your problem, and I found it interesting. I've been programming PLCs for a while, and never faced a problem like that, but in this case, I remember clearly the S24 properties that the manufacturer points out at their manuals (for DOS). Your comment is absolutely right!, then I want, this time, remark the importance of the methodology when the program is developed. The mathematical models must be as much similar to the real model as possible, and the PLC program must be structured and modular, but most important of all, developed using the functions and features of the device that the programmer already knows and understand completely. -How,otherwise, a programmer can be considered a PRO?