polymorphic_url with map.resource rails 2.3

In a rails 2.3 app when i do a polymorphic_url with a model that is
mapped with map.resource instead of map.resources I am getting a funky
url

"http://test.host/first_aider.%23<firstaider:0xb6f12578>"

where I want
http://test.host/first_aider

is there a valid way to do this

cheers

Stephen