Suspects and prosecution or defence witnesses may share the same household, work together or come in to contact in any number of ways, and in england-and-wales (which has a comparable criminal justice system to new-zealand) there is no law per se preventing them from talking with each other - unless it involves intimidation, harrassment, perverting the course of justice, or the suspect is subjected to specific bail conditions preventing any and all contact with a witness or witnesses.
(1) A person commits an offence if—
(a) he does an act which intimidates, and is intended to intimidate,
another person (“the victim”),
(b) he does the act knowing or believing that the victim is assisting
in the investigation of an offence or is a witness or potential
witness or a juror or potential juror in proceedings for an offence,
(c) he does it intending thereby to cause the investigation or the
course of justice to be obstructed, perverted or interfered with.
conduct to persuade any person not to do something that they are
entitled or required to do, or to do something that they are not under
any obligation to do.
conspire, act or embark upon a course of conduct which has a tendency
to, and is intended to pervert, the course of public justice.
(NB in England and Wales there is no such thing as attempting to pervert the course of justice - it's either done or it's not.)
Also, the Prosecution and Defence, the former usually via the police, may:
interview each other's witnesses or prospective witnesses; and May
take statements from those witnesses. However, each party must ensure
that no attempt is made to persuade the witness to change his/her
Interfere appears six times in the England and Wales Bail Act 1976 - five in the phrase "interfere with witnesses or otherwise obstruct the course of justice" and once in "where defendant may fail to surrender to custody, commit offences on bail or interfere with witnesses". It, or its various forms, also appears nine times in the New Zealand Bail Act 2000 in a similar context which, in my opinion, implies a nefarious or illicit action distinct from "just having an innocent chat."
Interfere is not defined by either Bail Act, so the convention applied by the UK courts is to use the common everyday meaning by reference to the Oxford English Dictionary. Such definitions include to intervene in a situation without invitation or necessity and to prevent (a process or activity) from continuing or being carried out properly.