custom lead fields not mapping values after using lead conversion class

Question

I created a javascript button that will convert the current lead to a contact based on conditions that I've sent. It works as expected. The problem I have is the custom fields from the lead are not mapping to the contact after conversion.

The mapping

The apex code the converts the lead

try{
    // query a single contact that has the same first/lastName and email as the lead,
    // and marketo sync is true.
    // the contact will be the one that was last modified at the closest date to 
    // today.                
    Contact c = [SELECT Id, AccountId, OwnerId
                 FROM Contact 
                 WHERE (Email               = :l.Email
                        AND FirstName       = :l.FirstName 
                        AND LastName        = :l.LastName
                        AND Marketo_Sync__c = true
                        AND Owner.Profile.Name IN :profileNames)
                 ORDER BY LastModifiedDate DESC
                 LIMIT 1
                ];

    // if matched contact found, update the contact owner to be
    // the same as the lead owner
    c.OwnerId = l.OwnerId;
    update c;

    Database.LeadConvert lc = new Database.LeadConvert();
    lc.setLeadId(l.Id);
    lc.setAccountId(c.AccountId);
    lc.setContactId(c.Id);
    lc.setDoNotCreateOpportunity(true);

    LeadStatus convertStatus = [SELECT Id, MasterLabel FROM LeadStatus WHERE IsConverted = true LIMIT 1];
    lc.setConvertedStatus(convertStatus.MasterLabel);

    leadsToConvert.add(lc);

    // throw an error if the contact soql fails
}  catch (QueryException e) {
    mergeErrors.add(e);
    System.debug(e);
}

Database.LeadConvertResult[] lcrList = Database.convertLead(leadsToConvert, false);

Answer 1

This is expected, as noted in Considerations for Converting Leads:

When updating existing accounts or contacts during lead conversion, the values of mapped lead fields do not overwrite the values of the mapped account and contact fields.