USER username mode unused :info
is the syntax according to RFC 2812. IRCD 2.11 extended this a little.
You can check how would IRCD interpret mode parameter:

Fatal error: Uncaught Error: Undefined constant "bits" in /home/bif/public_html/ircd/userbits.php:18 Stack trace: #0 {main} thrown in /home/bif/public_html/ircd/userbits.php on line 18