Auto-detection is a heuristic approach to try to detect which fractions are needed by the user code/application. It has been improved a lot and we will probably see more improvements in the future but due to it's nature there might always be false-positives here and there.
As outlined in the linked Google groups discussion, it would come in handy if one could prevent an auto-detected fraction from being added to the deployment/fat jar.
This could either be done by introducing a negating prefix like "!" in the fractions parameter of the plugin or by introducing a new parameter like fractionExcludes.