We imported the contact's id from CTCT contact list as a data field in our local database. The utility we have setup to Synch the two databases also checks to see if the contact's id already exists on our file, and if it does, is it the same.
I really didn't expect to see any reports of contact's id changing - but so far I've seen it happen twice now today.
It's not an issue - just more curious what would cause it to change?
What you are seeing should only be possible if there are duplicated contacts in the Constant Contact account. In the case of duplicates, the API can only return a single result when searching by email, and it will return the oldest of the contacts which match the search. In this case, it sounds like you have stored a contact ID for a specific email which is not the contact ID that is returned on a search for that same email.
You can try searching for these contacts that you're seeing in the UI to check if the duplicated contacts are all active. If you don't find any results there, we could help you investigate via email so that details such as email addresses can be shared.
Please let me know if you have any questions!
If I use the API and give both Contact Ids, I get two different email addresses - although - they are the same name.
I'm not too concerned at this point - I'll have to keep an eye, and see if I can see any patterns.