I have a perl script that has worked well for years.
It uses the V1 API to retrieve a list of all members of a particular list. It then feeds the result to a mailman list we maintain for daily reports. We run this script once per day.
Usually when it runs the constant contact list and the mailman lsit differ by only a couple of names. However, since OCtober 4, it has been reporting inconsistent results, removing 400 names one day and adding 1950 the next.
I reported this exact same issue January 3, 2012. Ryan Davis verified the error, and a fix was released:
Response Section Response (Ryan D) 01/24/2012 07:40 PM Hey Wesley,
We have released a fix for this issue as of today. You should receive accurate results from the list members collection.
If you have any questions please let me know.
I'm seeing this too from a C# client we use. I record the nextUrl link in my logs and the web service keeps repeating the same nextLink over and over again.
Thank you for reporting this issue. We have received a few other reports and we currently have a senior engineer working on this issue so that we can resolve it as quickly as possible. I hope to have a status update with an expected timeframe available soon.