The way to trouble shoot it is to view the css. I would enable combining but disable minifying so that the css is easier to read and look for anything malformed or incorrect, possibly you missed something in fixing the quoting. View the source of the page and then click the link for the css handler to view the css,look for anything unexpected or incorrect.
Keep in mind that you can only control caching when using the combiner, if they are not combined then the browser may cache the static css files and changes may not appear until the browser cache is cleared. To clear the browser cache you need to not have the site open because it won't clear the cache for a page you are currently viewing. so go to google or something, clear the cache then come back to the site.
Hope that helps,
Joe