I'm using the REST api to add and remove contacts from contact lists. I have everything working just fine, with one rather strange caveat: The first time I try to update a contact's lists, they end up removed from all lists on Constant Contact. When I execute the request again, with exactly the same data, the contact lists 'take,' and they are added to / removed from those I passed in. I've made certain that the XML passed in in each instance is identical. Anyone encountered this before?
As long as you are putting in the Contact Lists when you do the PUT, it should not remove them. Can you show me the XML that you are using when you do the initial PUT request that updates the contacts?