Rails - multiple forms unintentionally using the same object - ruby-on-rails

Question

I've got a page showing details for every #user. Each user has an enrolment, which can has a comment. When I e.g. do this:
<% #user.each do |u| %>
<% the_enrolment = Enrolment.where(user_id: u).first %>
<% end %>
Then in every iteration the enrolment is a different enrolment, as the user changes in every iteration. So far, so simple.
But when I pass this enrolment variable (while looping through) to a partial which contains a form, like this:
<%= render 'the_partial', enrolment: the_enrolment %>
With this form (in the partial view):
<%= form_for enrolment, :url => the_path, remote: true do |f| %>
<%= f.hidden_field :id %>
<%= f.text_area :comment %>
<%= f.submit "Save" %>
Then, in the finally rendered page, every form uses the same enrolment. (They all have the same id and every text_are is pre filled with the content of one of them. What am I doing wrong here?
The complete iteration looks like this:
#user.each do |u|
the_enrolment = Enrolment.where(user_id: u).first
<%= the_enrolment %> # correct id
<%= render 'the_partial', enrolment: the_enrolment %>
end
Thank you very much!
Update
Here is an update with the newest informations. The problem seems to be that the form is placed inside a twitter bootstrap modal. Here is the whole partial:
<%= enrolment.id %> # here it's the correct id
<div id="myModal" class="modal hide fade" tabindex="-1" role="dialog" aria-labelledby="myModalLabel" aria-hidden="true">
<div class="modal-header">
<button type="button" class="close" data-dismiss="modal" aria-hidden="true">×</button>
<h3 id="myModalLabel">Admin Comment</h3>
</div>
<%= form_for enrolment, :url => the_path, remote: true do |f| %>
<div class="modal-body">
<p>
<%= "enrolment in modal: #{enrolment.id}" %> # at this place the id is ALWAYS the id of the very first enrolment
<%= f.hidden_field :id %>
<%= f.text_area :comment_admin %>
<button class="btn" data-dismiss="modal" aria-hidden="true">Close</button>
<%= f.submit "Save", class: "btn btn-success", id: "admin-comment-submit-button" %>
</p>
</div>
<% end %>
</div>
If I delete everything on this page concerning the modal, the form works.