When you use tools like Live HTTP Headers, they show you the actual HTTP headers sent by the browser. What they do with meta
tags used to simulate HTTP headers is a different issue. We can expect any conflict to be resolved in favor of the actual headers. (This has been normatively specified in HTML specs for Content-Type
headers.)
To control cacheing, you should (at least primarily) use server configuration. See Caching Tutorial for Web Authors and Webmasters.