Mergefields: Strange behaviour on agreement with multiple template

Hello,

I'm trying to figure out how is working the merge process while creating a multi template agreement using REST API, my scenario is the following:

1. Using the website I create two template(template1 and template2) with two readonly data fields type "Text Input" named respectively, customerName and customerSurname (in fact I do have the need of repeat that fields value in more than a template) 
2. Using API I create an agreement using both templates and passing a mergeFieldInfo array with customerName="John" and customerSurname="Doe"  
3. [Here come the problem]Only the data fields on the first template are correctly replaced/updated and all other fields are completely ignored.

After a brief investigation I've retrieved the agreement fields (using the API  https://secure.eu1.echosign.com/public/docs/restapi/v6#!/agreements/getFormFields) and I've observed that the name of the second template fields are changed appending an apparently random "_n" where n is a 2 digit number. 

Now the questions:

• Which is the correct way to handle this scenario?
• Is it possible to keep the relation between template Field Names and the new names generate in the agreement fields list?

Thanks in advance 

Best regards.

Pietro