Convert Lead fails when "Checking Duplicate Email Address" feature is enabled for contact module

Convert Lead fails when "Checking Duplicate Email Address" feature is enabled for contact module

I'm trying to convert lead using api method  https://www.zoho.com/crm/help/api/convertlead.html

While account and contact already exists then i'm sending also associated accountid and contactid.

Example request 
  https://crm.zoho.com/crm/private/json/Leads/convertLead?version=2&scope=crmapi&leadId=1479825000000089009&authtoken=xxxxxx&newFormat=1&xmlData=<Potentials><row no="1"><option val="createPotential">false</option></row><row no="2"><FL val="ACCOUNTID">1479825000000088001</FL><FL val="CONTACTID">1479825000000089005</FL><FL val="OVERWRITE">false</FL></row></Potentials>

And the response for this request is 
{"response": {"uri":"/crm/private/json/Leads/convertLead","error": {"code":4819,"message":"Duplicate record(s) with same email address already exists."}}}