PHP BUG??? Cannot figure out why this throws warning

PHP BUG??? Cannot figure out why this throws warning

I kept getting this on "Quitter España" (which seems to be the name
causing the commotion, as it's part of this sprintf algorithm):

   PHP Warning:  sprintf(): Argument number must be greater than zero
    in /srv/www/vhosts/quitter.es/%/htdocs/lib/action.php on line 1175

I'll just make it quiet for now so it doesn't spam other sites with
UTF-8 characters in their name (if that's what's causing this).