I suspect that you're not doing quite what you think you're doing.
Run frobiz: , then see if that's in your history. Frobiz should normally fail - there's no such command. But it will be in your history. I suspect that you are trying something like ls *![0-9], which will fail with
base ![0-9]": event not found
The thing is; when failing like this, bash never attempts to run the command, so it doesn't get put into the history.
IGNOREBOTH is irrelevant to this - it works as advertised. Try escaping the ! (which the shell is taking to refer, ironically, to a command in the history) - eg:
ls \! ...
And it will probably work as expected.