Are you on 4.0.12? If so, a known bug is present in that version that makes it impossible to save a group's settings once they've been changed. In order to get this one fixed, you would need to upload a patch that fixes the issue. Unfortunately, said patch doesn't seem to be available on IPS's community site anymore. Since that's the case, you're gonna want to simply upgrade to 4.0.13(.1) and just have it fixed for good.