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I tried doing it and I can see is possible to import data into a cloned form, but you should ensure you are uploading a file with the fields as required by the import app.
Here is the guide to import your submissions : http://www.jotform.com/help/308-Import-App-Easily-import-your-Excel-or-CSV-data-into-JotForm
Your form must be the same, with the same fields and names.
Do let us know if you need more help, we will be glad to assist you.