To reproduce: 

• Add to configuration a custom tosca function of type "get_input"
• Create a service, and a resource to the service
• Set a property on the resource using the custom function
• Export the service
• Import the service
• The property is represented in the UI as a string in the new service, and is not opened as a tosca function when the tosca function button is selected

Also, if using an index, the value is represented as a string instead of an integer after import