Qtranslate redirect homepage with W3TC

I am using the Qtranslate (multi-language) plugin alongside W3TC, and everything is working fine except one small detail. Qtranslate has an option to redirect a visitor from the “frontpage” to a specific language based on detected browser-language, but W3TC is interfering with this functionality, so I had to disable the “Cache home page” (page cache) setting in W3TC.

The site in mention is here:
football-island.com
If you set your browser to “Thai”, it will correctly redirect from the homepage “/” to “/th”, but at the cost of disabling “Cache home page” in W3TC. Any idea what this can be?

It took a good deal of diagnosing to figure out exactly where the issue lay before disabling cache for home page. Strange enough, the redirect works fine even with cache enabled on homepage (after emptying W3TC), until one clicks to go back to the default language. Thereafter, homepage is always stuck on default language and refuses to redirect (until I disable cache for home page). It is not related to cookies either, because I have disabled cookies in browser for testing and to force browser language redirect regardless of cookies …

Thanks for any help!