API uploads removing previous list information
When using addOrUpdateContacts as an API Call, it would be really helpful to just update the contacts information without removing it from all current lists (or perhaps have remove from current lists as an option instead of a standard).
This is something that is present when uploading a CSV file, but does not reflect on API sessions.
In late 2016, Bronto released a function, addOrUpdateContactsIncremental, where providing an array of listIds (or not) merely adds that contact to those lists instead of treating the array as wiping away any previous list membership.
Here is some more documentation about that API call:
Thanks for your submission and do please let us know if you are requesting something different!
Eric @ Bronto