As far as I can tell from the code, this template is being added to the cache. What page did you see it uncached on? If vw-general-ie7.css is not being reported as uncached, then this leads me to believe that the template vw-general-ie6.css is missing on your install. This could occur if you did not complete the upgrade process. When you upgraded, you went through the upgrade steps that replace plugins, language, templates, help, cron, etc?