I myself have never tested the -1 value so I can't tell you of all the issues if there are issues.
The problem with what we have now is you can make user groups so complicated that it can become very difficult to keep up with.
To me it would be simpler to keep up with by setting troublemaker permissions the same as user except for post moderation and then delete the member from users.
Of course I don't know the whole picture of what you are trying to do with all of your groups.
Other than that I think you need to put it all down on paper and compare permissions before you start changing them. It may show something you overlooked.
BTW I thought you copied the user group permissions to trouble maker anyway. At least that is what you said.
