file_create_url() get a wrong URL when default language use a prefix and file system is private

My drupal instance is set :
- to serve files using the private file transfert,
- to use prefixes for all active languages.

French is default and use "fr" and English use "en".

file_create_url('sites/default/files/test.png') returns 'fr/system/files/test.png' instead of 'system/files/test.png'

There is a patch to fix this bug. I hope there won't be side effects.