[Plugin: W3 Total Cache] Minify Question

I must be missing something obvious. I am not able to use the relative link syntax when specifying files on the minify tab.

For example, I’d like to use
//wp-content/common/css/site.css instead of
http://www.domain.org/blog/wp-content/common/css/site.css

When I save the changes on the admin screen, all leading forward slashes are stripped leaving wp-content/common/css/site.css

I’ve turned off all plugins but cannot find the cause. Any idea what may be causing this?

Thanks.