With debugging set to on,

```
define('WP_DEBUG', true);

```

my instance of WordPress doesn't show any debugging info.

After a lot of searching I figured that after I call `wp_debug_mode()` debug info shows correctly.

Can anyone tell me why calling `wp_debug_mode()` is necessary, since the debugging [documentation page](http://codex.wordpress.org/Debugging_in_WordPress) doesn't even mention this function?

Is there something in my environment that is causing this?