Rails I18n :many :other :count problems

I often have problems with translations. I remember this had to do with some translations using :many, but yet when I see an error message like this

translation data {:one=>"1 month", :other=>"%{count} months"} can not be used with :count => 3

...it shouldn't make any sense, isn't :other supposed to handle all other cases ??

EDIT for the english version, I'm using the default english files, so in this particular case, this one