I dunno, I never play with spell of making victory on, I have never been a fan of tech victories in these games, ever. I understand why the -9 is there, if you are close to the SoM the AIs should be aware and try to stop you, but ya it's totally broken right now because they all build the tower of the witch and they all go to war with each other because of it. I changed it in my files to be a +1 instead of a -9, I figure if they do fix it the forge would act as sort of a power symbol without the threat of the SoM.
I actually think I reported this bug shortly after FE came out though, or maybe I at least noticed it but didn't realize how big an issue it was until I saw how quickly the other AIs get their towers up with the new UI element. I know this is the second time I've had to mod a fix for it on my end.