Incosistent behaviour: server error

Sometimes Restfulie is answering with "Restfulie::Client::HTTP::Error::ServerNotAvailableError: HTTP error 503 when invoking http://localhost:3000/baskets/22/baskets/22 via get" when preparing to receive a request that will return a 415. Stack:

from /Users/guilherme/.rvm/gems/ruby-1.8.7-p249/gems/activesupport-2.3.5/lib/active_support/whiny_nil.rb:52:in `method_missing'
from /Users/guilherme/.rvm/rubies/ruby-1.8.7-p249/lib/ruby/1.8/net/http.rb:1060:in `request'
from /Users/guilherme/.rvm/rubies/ruby-1.8.7-p249/lib/ruby/1.8/net/http.rb:772:in `get'
from /Users/guilherme/.rvm/gems/ruby-1.8.7-p249/gems/restfulie-0.7.0/lib/restfulie/client/http/adapter.rb:221:in `send'
from /Users/guilherme/.rvm/gems/ruby-1.8.7-p249/gems/restfulie-0.7.0/lib/restfulie/client/http/adapter.rb:221:in `request!'
from /Users/guilherme/.rvm/gems/ruby-1.8.7-p249/gems/restfulie-0.7.0/lib/restfulie/client/http/marshal.rb:65:in `request!'
from /Users/guilherme/.rvm/gems/ruby-1.8.7-p249/gems/restfulie-0.7.0/lib/restfulie/client/http/adapter.rb:355:in `get!'
from (irb):14

In order to reproduce, execute the following with a content type that Restfulie client understands, but server is unable to produce:

Restfulie.at('http://localhost:3000/baskets/22').accepts('application/atom+xml').get!