I have noticed recently that when I run Generate Attachment Match Table from ArcCatalog, I am getting more records than I expect. For example, I have 5660 image files in my directory and all have a match back to my feature class. I would expect the same number of records to appear in the output Match table. However, I end up with about 5699. I was puzzled by this until I started looking at the Match table more closely. It looks like it is randomly creating duplicates of some of the match records.
The only way to quickly fix this is to convert the match table to Excel, remove the duplicates, and export back out to a table again. I can then use the new table without dups to add attachments to the feature class.
Is this a bug? I could not find anyone else who seemed to be having the same issue.