I apologize in advance if this has already been answered and I just didn't see it when I searched for it. Also, I will mention that I, myself, am not a FileMaker user. I provide IT service and one of our clients is a heavy FMP user that has been experiencing these issues since updating to FMP13 (previously on FMP12).
The client has two working files. One is a template used to send bids to their clients (often multiple bids per project) and once their clients have gone through and selected what they want from the various bids, individual data from those bids is imported into their main working file. For some reason after upgrading to FMP13, when they go to merge data from one of their numerous 'bid' files into their 'main' file, they often run into an issue where instead of FMP saying 'merging 1 of 1' it will pull from every single 'bid' file from the company's history. So if they aren't paying attention to the 'merging 1 or 1' field, it may say 'merging 1 of 12000' and will import everything from those ~12000 files.
They are working off of FMP files on their server. Each person has their own machine on the same network that has access to these FMP files. It should be mentioned that this importing problem does not occur when working directly on the Mac Mini server. Everything seems to work just fine there. All three of their personal machines on the network experience the problem and it is random, so I know the problem is not machine or user specific.
I'm sorry if I'm not describing the issue clearly. Not being a FMP user myself, I'm just kind of playing the 'man in the middle' in hopes that someone on these forums has seen such behavior and hopefully has a fix for it.
Thanks in advance for any potential help.