Rails - Nov 2005 - observe_field with form

i have 2 <div> blocks, each which have a form select box.  I have an 
observe_field watching the first dropdown, and populating data from the 
second one when the first changes.  The issue is when i change the first 
dropdown, the second form element doesnt get submitted any more after 
clicking on the submit button, and doesnt appear in the "@params" hash
any longer.  Any idea why this would happen?  The data all looks correct 
in the form,  even after changing dropdown options, just the field 
(os_versions) seems to "disappear" after submitting the whole form,
and
only when changing the OS select box.

here is my snippet:

    <div align="left" class="addnode_item">&nbsp;
       <select name="os" id="os" >
         <% @systems.each do |s| %>
           <option value="<%= s.id %>"> <%= s.osname
%> </option>
         <% end %>
         </select>
     </div>

      <%= observe_field "os", :url => {:action =>
"get_os_versions"},
:update => "os_versions", :with => "''os=''
+ escape(value)" ,:loading =>
"os_versions.innerHTML=''<font color=green> Please wait while
finding OS
versions....</font><br><br>''"%>

     <div align="left" class="addnode_item"
id="os_versions">
        <% if @os_id %>
         <%= render_component(:action => "get_os_versions",
:params => {
"os" => "#{@os_id}" }) %>
        <% end %>
     </div>


thanks
adam