Exporting vbOptions in Products

[phlogiston]

I've found this a wee bit unintuitive so thought I'd ask the cleverer folk here about it.

When including new custom options with a product, they don't get exported unless they are set yes to "vBulletin Default (Will be replaced by upgrade scripts)".
In the past when I've created my new options I've always set that to "no", because my custom options are not default vbulletin and my understanding was that any non-default options would be ignored and left as is by upgrades.
But when migrating products from my test site to live site I originally lost those options as they weren't in the product xml.

So can someone clarify what the difference is between setting "vBulletin Default" to yes or to no for me?

Part of me is half thinking this may be a bug because I'm not certain why I would have an option not exported with it's associated product :S