Custom Field Sets- Only the first CFS added to the Form can send data to CRM- data is sent to Case only

There is no problem when one CFS is attached to a Form- data is stored in case and in CRM.
When more than one CFS attached to a Form:
Expected behaviour: data to be stored in case and CRM.
Actual behaviour: data from both CFSs stored in Case. Only the first Custom Field Set's data is sent to the CRM- all fields from the second one are invisible in the Admin tab.