The stability checks were added as an afterthought to the program. They are not currently included in the optimization routines.... If we were writing the program from scratch today then that's not how I would do it. However, that's what we've got for now.
Maybe when we release a version 4.0 then it will have optimization for OTM and sliding as well.
Some additional thoughts:
1) When using the 0.6DL + WL Load combinations, the safety factor need only be 1.0. That's becasue the 1.5 factor of safety has already been account for with the reduced dead load.
2) Personally, I'd like to see us both optimize for OTM stabiliy AND allow the user to adjust this factor on a per LC basis. I know that my old company used to apply higher factors of saftety when DL or LL cause some overturning. Also, we used to use different factors of safety for wind and seismic.
Josh