Silliness? Check.
I was able to produce my own “can’t save server vars” error message, which is helpful. No such luck with the group permissions, though, which is how I came upon the theory that it just wasn’t displaying them correctly. It hadn’t struck me as odd that all of the checkboxes were blank until recently, when I remembered that a few of the groups get some basic permissions automatically. It took me quite long enough to then realize that my template did not even have the conditional check to determine whether each checkbox should be checked. However, trying to change the permissions doesn’t seem to save anything, and no error is given. I have a hunch that nothing is being saved because the plugin doesn’t have the proper privileges, an idea that I’ll have to go over with Jeff, along with parts of the API.