Well my thinking is if you correct the issue with bill not having mod tools there will be no need to allow users not to delete
i didnt realize that you were giving physical delete to mods i ran into issues years ago when i allowed that option to my staff and same issues arose so i decided to only have admin have those powers and i have never had a problem since but each forum is different .
i have also had issues with modifications causing secondary permissions issues like this where it gives users mod powers cause the way the coders coded the mod the scripts were off . the pia on that is you have to turn off each modification one by one till you find the problem one