Can't get it working in 3.8.1

OK, after restoring the whole website to what it was a week ago, I noticed that WP 3.8.1 had nothing to do with it.

In fact, it was because I also updated Poly Lang in the process, and it seems a new caching option was introduced.

So what I needed to do was to put

define('PLL_CACHE_HOME_URL', false);

into wp-config.php as specified here: https://www.ads-software.com/support/topic/multiple-domain-configuration-1