Edit is not working properly for radio_button

Hi,

I m trying to edit contact info.. all other data other than radio button
are getting reflected in edit page .. But the same works fine while
creating new contact i.e it allows only one email id to be set as
primary but the same not working in edit.. it allows user 2 select both
radio buttons
the view code is as follows
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<table cellpadding="4" cellspacing="0" border="1" width="100%"
class="details">
<tr> <th colspan="4" align="left" bgcolor="#797ba8"><strong><font
color="fffff">Email Addresses</font></strong></th>
</tr> <tr> <% i= 0 %>
   <% for email in @contact.emails %>
   <% fields_for "contact[email_attributes][]", email do |e| %>
   <td nowrap class="formLabel">Email <%= i=i+1 %> </td>
   <td > <%= e.select ('email_type',%w{Business Personal},
:include_blank => false) %>
   <%= e.text_field :email,:size=>"35",:maxlength=>"80" %>
   <%= e.radio_button('isprimary', "1") %>
   </td> </tr>
<% end %> <% end %></table>
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