1. 1. Context

I discovered this misbehaviour working on a settings.php, where I need to use an admin_setting_description to show some parameterized string. I suppose it will work the same way in other parts of the Moodle.

1. 1. Scenario

Supose the string 'a' of the component 'b' is of the form "{$a}<br/>Some kind description".

1. 1. What works properly

get_string('a', 'b', 0) returns a string like "0<br/>Some kind description", replacing the given value inside the string.

1. 1. What doesn't work

new lang_string('a', 'b', 0) return a string like '{$a}<br/>Some kind description", without replacing the given value inside the string.

I do not know if any other cases with similar behaviour may produce similar side effects (like working with booleans or empty strings or so).