Strange, my solution would be to make sure that you don't have the same number listed either in international format or in your normal local format saved on another contacts details.

Basically search through your contacts on the N9 phonebook to make sure theres not a duplicate of the number either international or local format

If there is a duplicate, deal with it, as Wazapp will act like the default call and text interface and just show the number as its linked to more then one contact card.