If it's just that one config style that's not loading up, I'm inclined to think there's nothing syntactically wrong with the custom_config.js, but the values you're giving it might be incorrect. Could be that you're trying to load a plugin/button that doesn't exist, or there's a typo, etc. That's where I'd look anyway. Barring that, maybe the browser has cached a previous version of custom_config.js that did not contain a description of "custom1", or crack open firebug cuz you've likely got a JS error of some kind coming up.