Yes, we know this issue well and it's happened to us 3 times since we "upgraded" from v14 to v15 last October. We've had a number of tickets opened and SmarterTools has been pretty unresponsive about getting this fixed now that all of the devs appear to be working on v16. Overall the situation sucks and we're looking at moving to Exchange.
We've supplied ST support with lots of info including videos that show the problem, screenshots that show duplicate entries in the Outlook GAL SharePoint list, errors we've found in the GAL SharePoint list using MFCMAPI (https://mfcmapi.codeplex.com/
), etc. but have seen little to nothing in return. This is a completely unacceptable bug with significant confidentiality issues. We've had the wrong staff receive salary and compensation communications. And the worst part is that it's completely unpredictable--we're at the point where we have ZERO confidence in the product. Other than the "sorry for the inconvenience" token response, support has done little more than to tell us there's nothing they can do because all of the devs are working on getting v16 out the door.
We've been a happy customer since 2008 and it's pretty disappointing to get kicked to the curb this way.