Having a weird devise problem.

The code looks like this:
%ul.nav.nav-tabs
%li.active
%a{ :href => "#log_in"}
=t :log_into_your_account
%li
%a{ :href => "#"}
=t :not_yet_registered
.tab-content
.tab-pane.active#log_in
%h2 Sign in
= semantic_form_for(resource, :as => resource_name, :url => session_path(resource_name)) do |f|
= f.semantic_errors
= f.inputs do
= f.input :email
= f.input :password
-if devise_mapping.rememberable?
.clearfix
= f.label :remember_me
.input
= f.check_box :remember_me
= f.buttons do
= f.commit_button :button_html => {:class => "btn btn-success"}
= render :partial => "devise/shared/links"
Generally speaking, how would I go about diagnosing things like that?
There was a bug in the gem. Fixed now.