Folder Exclusions and Heruistic Detections

I have a question about Heuristic detections. We have a folder exclusion in place to prevent detections for a piece of software. So far this has worked great for several years now. However starting about a week ago the clients started picking up a file in this folder and classifying it as Trojan.ADH.2. I'm not clear as to why the client is targeting this file because the folder has been excluded. In the log the file location specified is the excluded directory so I'm not sure how this is happening. Any Ideas?